Distributed temperature (DTS) and distributed acoustic (DAS) fibre optic sensing are now commonly used as key reservoir surveillance tools. This work shows the benefit of continuous downhole monitoring during the lifetime of a well. Fibre optic cables were permanently installed in a doublet injector/monitor well system as part of a CO 2 controlled released experiment at the In-Situ Laboratory in Western Australia. During the completion and injection operations various planned and unplanned events (mud circulation, cementing, drilling, wireline logging, gas and water flows) occurred. The events were monitored from surface to reservoir with DTS and DAS fibre optic cables. The DTS was recorded continuously data starting during well completion throughout the lifetime of the wells while DAS was recorded at specific points in time, mostly associated with borehole time-lapse seismic acquisitions. For the well completion stage, the interpretation of the DTS dataset acquired during mud circulation provided information about thief zones above the reservoir. During cementing and cement hydration, DTS highlighted areas of large breakouts and confirmed cement in-fill in those intervals. During the drilling of an unexpected cement infill, it provided a unique insight into downhole progression of the drill bit. During the CO 2 injection stage, DTS enabled monitoring the phase behaviour at the injector using distributed temperature data combined with a permanent pressure downhole gauge. At the monitoring well, the injected gas breakthrough was clearly detected at reservoir level within 1.5 day after the start of injection. Moreover, the accumulation of the CO 2 over time was captured accurately at reservoir level for a further 3 days. During an unexpected leak in the casing, gas from the reservoir started entering the monitoring well leading to cyclic release of water and gas at the surface. The DAS dataset enabled to pin-point the exact moment the casing leak occurred while the DTS dataset captured the cyclic nature of water and gas leakage. The sensitivity of the tools and interpretation methods are such that the downhole location of the event can be determined within 1 m and the timing within a few seconds. More importantly, the continuous and distributed recording allowed monitoring the events developing in time over the full length of the well. This work highlights the unique benefit of permanent distributed monitoring using distributed fibre optic sensing during the lifetime of a well. The continuous and distributed recording allowed monitoring events developing in time over the full length of the well and provides direct observations for the different events while providing near-real-time information about downhole processes.

Oil-based mud is commonly used in drilling of the pay zones in sandstone formations as a less/non damaging fluid. Oil-based mud typically contain emulsifier, viscosifer and other additives including polymer blend and calcium carbonate to serve different functions. Presence of emulsifier may increase emulsion tendency upon interaction with downhole environment. The resulting emulsion might be tight to an extent that a thick sludge is formed which can impair well productivity. Identification of the sludge material will help in development of an effective chemical treatment to remove formation damage and restore well productivity. In this study, an extensive laboratory work was conducted to explore potential interactions of an oil-based mud with different contaminants encountered in downhole environment. A typical sludge sample was characterized using different analytical techniques including solvent extraction, XRD, TGA, ICP and viscosity. The results showed that the sludge sample contained calcium carbonate, dolomite quartz as the main components in the inorganic phase while the organic phase include polymers and oil. The source of calcium carbonate might the drilling additives while the source of quartz is the formation. Analysis of supernatants generated from solubility tests conducted for the sludge sample revealed in addition to the high amount of calcium presence of iron in considerable amount (nearly 1,000 mg/L). Interaction of ferric chloride, quartz with an invert-emulsion mud was investigated. A significant increase in viscosity was observed upon incorporation of these contaminates with the mud sample. This paper presents in detail the results of interactions of iron ions, quartz, and pipe dope. It also examined several chemical formulations for removal of sludge formed and filtercake.

Tubular engineering design is essential for production operation, especially in the mature oil and gas fields. The complex interaction among oil, natural gas, and water, complemented with wax, scale, inorganic compound, and deformation brings complexity in analyzing tubular integrity. This challenging problem will be more severe if the wells are located in offshore environment, therefore finding the cause of tubing deterioration is a challenging. Field X, which has been in production for 30 years, cannot avoid the possibility of tubular thinning and deformation. The degradation is slowly developed until severe alterations are observed on the tubing body. The current state of the wells is complicated since the deformation inhibits the fluid flow and increases the risk of wellbore collapse and complications during sidetracking, infill drilling, workover, and other production enhancement measures. The risks can be harmful in the long run if not mitigated properly. The current condition encourages us to conduct more comprehensive study on tubular degradation. It is to model the multiple degradation mechanisms, such as corrosion, scaling, and subsidence, under the flowing formation fluid. The model is then coupled with reservoir simulation in order to provide a better outlook on tubular degradation. We used multiple case studies with actual field data to identify the dominant mechanism on tubular degradation. The case study cover various reservoir and fluid characteristics and also operations problems to develop general equation and matrix for risk analysis and field development considerations. We present the degree of tubular degradation and its effect to overall field performance and economics. Current field practices do not encourage a thorough tubular assessment during early life of the wells, which create complex problem at later stage. The study indicates that a proper planning and preventive action should be performed gradually before tubular degradation becomes severe. The paper presents a field experience-based model and guideline matrix that is useful in developing new areas from the perspective of well and facilities integrity, so that the degradation-related issues could be recognized earlier.

Poor conformance & injectivity sustenance is a major concern of Mangala, Bhagyam & Aishwarya (MBA) fields. The presence of high permeability streaks or thief layers between injection and production wells typically results in pre-mature water breakthrough, high water cut and deficient volumetric sweep. As a result, significant oil volumes in the reservoir may not be contacted by the injection fluid. Another concern is of low VRR (Voidage Replacement Ratio) in some of the layers due to reduced injectivity in those sands. Consequently, it has led to poor recovery from those sands. It is also a growing problem with the polymer deposition taking place in the wellbore particularly Mangala (undergoing full-field polymer flooding), leading to challenging wellbore cleanup operations. Several methods have been used in the past, both mechanical and chemical to improve the treatment fluids during stimulation. In this paper, we introduce a novel technique; Radial Jet Drilling (RJD) for Injection & Conformance Improvement which is practical & effective and has resulted in injection improvement of greater than 100% and at-least 3x sustained treatment result over conventional techniques performed earlier. The technique involves running in hole the RJD deflector shoe on jointed pipe (typically 2-3/8") to the target depth & correlated. This is followed up with high pressure coiled tubing to rig up over the jointed pipe string and perform operations in two steps: Milling to establish Casing exit Jetting to create lateral of desired length (30 to 100m) Both operations require separate runs with different downhole assemblies on coiled tubing. The setup allows the operator to jet with fluid of choice depending upon the geological & well fluid understanding. The selection of depths to create desired laterals depends upon sand thickness, formation dip, sand continuity, well deviation, cement quality & few other factors which shall be discussed in this paper. As a result of the created laterals, the injection fluid experiences low pressure drops and bypasses damaged zones/permeability barriers; which ultimately results in improved injection & conformance leading to better sweep efficiency. The other advantage of the technique is the relatively easy integration of tool with existing infrastructure i.e. small horsepower rigs. This paper will document the physics behind the technique, treatment design considerations and implementation for stimulations performed across the fields using Radial jet drilling. Particular attention is paid to multiple injector well stimulation case studies from these fields, the challenges faced, the solutions implemented, results & inferences drawn using post job surveillance. The results observed across the field w.r.t injection & its sustenance performance is consistently greater over conventional methods used earlier.

Lost circulation is a major contributor to non-productive time (NPT). Any efforts to better understand the factors that lead to it and subsequently identify a suitable cure will translate to tremendous savings of time and money for operators. Conventional materials such as calcium carbonate, nut shells, graphites and fibers are successful in curing many cases of seepage and partial lost circulation. However, there is a practical limit to the concentration of these materials used to combat the most severe losses due to the limitation of pumps and drilling assembly. In porous formations, high fluid loss squeeze pills have seen some success in reducing losses by forming a high compressive strength plug, but these pills do not have a good success rate in large fractures or vugular formations. Such challenges are better addressed by cross-linking pills, but even this solution does not always have a high success rate due to the low compressive strength of the formed plug. The new phase-transforming loss circulation material (PTLCM) was designed to be pumped easily and achieve thixotropic behaviour under downhole conditions, resisting losses in the thief zone prior to setting as a rigid plug with high compressive strength. A setting-control additive ensures the LCM does not prematurely set. The additive is used at a concentration calculated by considering the time required for pumping and the bottom hole temperature (BHT) in the thief zone. After the LCM sets, a high compressive strength solid plug is formed that can resist fluid loss to the formation. The LCM has a high acid solubility of ~95%, making this system a viable option for deploying in reservoir sections, depending on the client requirement and well conditions. This paper describes two recent successful applications deploying this novel technology. Case Study #1: While drilling in sandstone, the well experienced total losses, which presented an immediate challenge to maintain hydrostatic pressure. The operator responded by pumping several conventional pills loaded with a broad particle size range of fibers, granules and polymers. These pills were unsuccessful at healing the losses, so the operator opted to deploy the new technology LCM. The losses were cured successfully with a single application. Case study #2: Wells drilled in the Western Desert have traditionally experienced severe to total losses while drilling fractured dolomite. Frequently, such events have been difficult to cure by conventional means. The only solution has been multiple applications of cement plugs to heal the losses. This case study describes a well with dynamic losses of more than 150 bbl/hr that were healed by spotting one pill through the circulating sub across the thief zone. The losses were successfully cured, allowing the operator to continue drilling.

Due to the long-term fluid-solid interaction in waterflooding, some sand particles forming the reservoir formation detach from the rock and migrate with fluid in the reservoir, which will cause many problems such as borehole instability and casing collapse. However, the mechanism for sand production process is not clear. Therefore, it is very urgent to find out the mechanism for this process. This paper presents a coupled lattice Boltzmann method and discrete element method (LBM-DEM) to study the sand production process of the formation. The method has been validated by simulating the sedimentation of single particle. Simulation of sand production process is conducted and the effect of cementation type, cementation strength and injection rate are investigated. During the simulation, sand particles will detach from the reservoir and the formation will reach a steady state after a period of time. Strong force chain rupture can be recognized, which is the main reason for sand detachment. Besides, force chain reorganization can be identified. The total number of produced sand first increases and remain constant after the force chain reorganization. Reservoir with clay cement produces more sand than that with carbonate cement. For the same cementation type, reservoir with lower cementation strength produces more sand than the higher one. Moreover, higher injection rate leads to more sand production than the lower injection rate. The proposed method presents simulations of sand production process at a pore-scale level which is the best scale level to describe the phenomena. Compared with experimental method, it doesn't need too much labor and can reveal the mechanism of this process. This method not only can be widely used in the study of sand production process but also can deal with other problems such as proppant migration in fracturing and gel particles migration in profile control, which is very important to the oil field development.

As the shale development activity in the Permian continues to be strong and oil prices recover, increasing numbers of infill child wells are being drilled as operators want to improve recovery from each section and continue to meet their production targets. However, production data suggests that both parent and child wells suffer from production losses if they are located too close to one another. The cube model concept, which is also referred to as supersize fracturing, was first introduced about two years ago and has been piloted in the Permian Basin. In a cube model, multiple wells, usually more than 30 horizontal wells with five to six wells in each different horizontal layer, are drilled and completed in the same section. Operators produce those wells simultaneously with the objective of mitigating the parent-child effect of unconventional reservoirs. Nevertheless, with all wells producing at the same time and competing for production from the first day, will this benefit ultimate recovery? This question was investigated through comprehensive fracture and reservoir modeling and simulation. A reservoir dataset for the Spraberry Formation in the Permian Basin was used to build a hydraulic fracture and reservoir simulation model. Different field development strategies were studied. Models representing a traditional parent-child scenario with five parent wells completed and produced one year before four infill child wells and a traditional parent-child scenario with five parent wells completed and produced five years before four infill child wells are compared. In these cases, a geomechanical finite-element model (FEM) was used to quantify the changes to the magnitude and azimuth of the in situ stresses from the various reservoir depletion scenarios. Next, a cube model with nine horizontal wells completed and produced simultaneously was analyzed. These three scenarios were expanded to include 19 horizontal wells with the same methodology. This study aims to help operators in the Permian Basin, as well as in other unconventional reservoirs to understand how different field development strategies affect ultimate hydrocarbon recovery and net present value.

In 1D Geomechanics projects, calibration of stress is extremely important in the construction of a valid Mechanical Earth Model (MEM). The minimum horizontal stress data is usually available from LOT (Leak-off test), XLOT (Extended Leak-off test), Open hole stress tests, or cased hole Mini Fall off Test (also called Diagnostic Fracture Injection Test – DFIT). These traditional measurements have a few deficiencies. This paper presents an application to a gas storage field, where stresses are derived from a newer unique approach where the radial variation of acoustic velocity from advanced dipole sonic logging tool is inverted to obtain stress. These derived stresses are then utilized to calibrate the 1D MEM for the gas field. This approach addresses some of the deficiencies of traditional approaches of deriving stress magnitudes. The characteristics of this approach are: Both the minimum horizontal stress (Shmin) and maximum horizontal stress (SHmax) are obtained. Traditional approach provides a value for Shmin only. These measurements are obtained in reservoir zones at multiple depth intervals. Traditional approaches provide a measurement at one depth only. This method is applicable to all formations that are acoustically stress sensitive. This method is relatively more cost effective as compared to traditional approaches where rig time is a premium considering that advanced sonic logs are routinely run for other applications as well. The sonic data was processed to derive a dispersion plot (velocity versus frequency). From this plot, a plot of velocity versus radial distance is derived. As Kirsch equation provides a radial variation of the stress with distance for a hole drilled in a uniform stress field, and variation of stress translates to variation with velocity, a parametric inversion is utilised to derive the stress. In this gas field, no LOT or XLOT were available. However, the advanced dipole sonic logging tool was recorded in a well recently drilled and some of the formations were found to be acoustically stress sensitive as observed from the dispersion plot. Therefore, this inversion technique was applied and Shmin and SHmax were obtained that were extremely useful to calibrate the 1D MEM. This technique is unique in the industry and complements existing methods to obtain stress measurements for 1D MEMs where stress measurements are either not available or expensive to obtain. This method is not widely used. The authors hope that this paper will illustrate how this method was used in this gas field and encourages other users to investigate the application of this method in their fields, when traditional data is limited.

The PEP structure in Matindok block in Central Sulawesi has been proven to produce gas reserves in the Minahaki formation based on the first exploration well PEP-001 that was drilled in 2018. The PEP structure has a Miocene carbonate build-up play, and the target reservoir is the M member pinnacle carbonate reef. One of the main challenges in this area is low resolution of seismic data, leading to a high depth uncertainty of top M position. The PEP-001 well was planned to set the 9 ⅝-in casing point above top M. Offset wells did not show any clear markers in the thick shale above M formation, that could have been used for log correlation. In previously drilled offset wells correlation was done conventionally by taking cutting samples and relying on drilling parameters break. However, when PEP-001 was drilled, no apparent drilling break was observed. By the time cuttings reached surface, the bit had drilled into 20-m thickness of M formation. Since casing covered most part of the upper carbonate formation, open hole logging and well testing data were not acquired to delineate target M formation optimally. The second exploration well PEP-002 was planned with an objective to set 9 ⅝-in casing ~5 m above top M to acquire a full interval coverage of coring, open hole wireline logging, and well testing program. This information was critical for optimal reservoir delineation to allow for accurate reserve calculation and future structure development. Conventional correlation (well-seismic pairing and correlation) has proven insufficient for casing point placement and was a lesson learned from PEP-001. The presence of limestone stringers observed in offset wells within proximity of top M presented an additional challenge. The stringers could have been mis-interpreted as the main carbonate body, if interpretation was solely based on cutting samples. Based on these challenges, a technology with the capability to map and detect lithology changes ahead of the bit in real time was required. Real-Time EM Look Ahead technology uses deep directional electromagnetic (EM) technique to detect formation feature ahead of the bit. A feasibility study was done to simulate the tool response and define the placement of transmitter and receivers (spacings) in the BHA, as well as frequency selection based on the resistivity properties from offset wells. Based on the simulation, this technology was expected to detect top M formation as early as 10 m ahead of the bit. While drilling, top M could be resolved at 6 m ahead of the bit with an uncertainty of <1 m, therefore making this the fit-for-purpose technology to place the 9 ⅝-in casing point ~5 m above the M formation. As a result, 9 ⅝-in casing was successfully placed 5 m above top M. High resistivity contrast, that is expected to be top M, was mapped continuously from 10 m ahead of the bit. The decision was to set the casing point at 1706 m MD, 4-5 m from the estimated top M. Coring results and open hole logging in the subsequent 8 ½-in hole section confirmed that top M was at 1711 m MD, 5 m from the casing point, which was precisely as estimated from Real-Time EM Look Ahead Technology. This technology also helped detect thin limestone stringer and differentiate it from the target carbonate formation. It prevented 9 ⅝-in casing to be set ~118 m shallower where the first limestone stringer was observed. This has avoided extra operating days in case of drilling problems due to long exposed shale in the subsequent 8 ½-in hole section. The potential cost savings were estimated at USD 1.35 million for an additional 6-in hole section. Following this success, the same technology will be used in the next planned exploration wells.

The strong domestic need for oil in China requires further exploration in unconventional reservoirs, such as volcanic and shale oil reservoirs. Sweet zone identification is one of the most critical missions in formation evaluation. The complex mineralogy and the low porosity in unconventional reservoirs result in little contrast of resistivities between oil-producing zones and water zones. Reducing uncertainties affecting the type of fluid in the reservoir and its potential movability is key to defining the optimal landing zones for future horizontal drains. In conventional reservoirs, nuclear magnetic resonance (NMR) logging based on cutoff analysis is the optimum choice for evaluating the porosity and pore geometry of hydrocarbon bearing reservoirs. However, the routine single-dimension T2 measurement is not sufficient for fluid typing in unconventional reservoirs because of the overlap of signals of various fluids in the T2 domain. This contribution presents case studies from a new generation NMR tool providing continuous 2D T1-T2 measurements. The T1-T2 measurements enable separation and quantification of different fluids in the pores. Fluid typing can be done by integration of other wireline logs such as spectroscopy and dielectric. Case studies are presented from volcanic and shale oil reservoirs in Xinjiang Oilfield of PetroChina. In the volcanic reservoir case, dedicated 2D data analytics technic is used to extract relevant signals from 2D NMR T1-T2 measurements. An integrated workflow combining wireline borehole electrical image, nuclear spectroscopy, dielectric dispersion and NMR T1-T2 gives an insight into the fluid composition in the pore system. Besides accurate measurements of lithology independent porosity and pore geometry from NMR, T1-T2 specific measurement of clay bound water volume and total water volume match well with the same measurements estimated from nuclear spectroscopy and dielectric dispersion logs. It lowers the uncertainties on fluid types in the volcanic reservoir where resistivities fail to differentiate wet zones and oil zones. In the shale oil reservoir case, a reservoir producibility index (RPI) derived from the integration of NMR T1-T2, wireline borehole electrical image, and nuclear spectroscopy is shown to be quite efficient in sweet zone identification and ranking. This paper discusses a novel application of a new generation NMR T1-T2 logging method in unconventional reservoirs, which helps the operator ascertain the potential of these reservoirs. The oil zones identified by the new method have promising oil productions. The workflow illustrated in the two case studies can be applied and extended to other unconventional plays in China.

One of the keys to successful and environmentally responsible well stimulation programs in coal seam gas development is to establish consistent procedures for the safeguarding, planning and executing activities across multiple wells. The aim of this paper is to show how a novel application of petrophysical program scripting can be used to make the stimulation process more efficient, consistent and compliant across assets with varying requirements. A macro embedded in petrophysical evaluation software applies a series of rules to rank coals by thickness, allocate a series of perforations and stimulation type based upon coal rank and spacing and then produces actionable treatment schedules which are seamlessly implemented in well stimulation operations at well sites. To do this, the macro grades all coals within the well by thickness based upon a cut-off on the density log, with the thickest coal being graded highest. The macro then identifies the top ranked coal and places perforations based on user defined logic, geological information from offset wells, permeability attributes of the target coal layer(s), depth and vertical separation between adjoining coal targets. Based on the stimulation type assigned, a stimulation schedule is generated that includes estimates of fluid volumes, proppant volumes, injection rates, proppant ramp type and stipulates flush conditions (over-flush or under-flush). Coals thicker than a maximum perforation size are perforated in an upper, middle and lower configuration. Most coals are thinner than the maximum allowable perforation interval and so the macro looks up and down the borehole to include thinner coals within a potential perforation window. The system then generates the stimulation schedule as described above. The macro continues to allocate perforations and stimulation schedules for each validated coal interval and sequentially tries to maximise the total target coal interval along the wellbore. Certain environmental constraints are included in the macro logic to maintain local and regional commitments. For example, coal zones in proximity of permeable non-coal layers i.e. interburden are automatically excluded from stimulation. Multiple advantages of this system have been realised including, a) effective QA/QC as outputs can be directly plotted against the well logs giving the user a quick and easy visual check b) actionable instructions that site based teams can execute including exact perforation depths and stimulation schedules c) provide realistic materials and costs estimates that ensure efficient planning and logistics, d) monitor and document any variations between allocated schedule versus actual execution, e) provide estimate of expected net coal connectivity at a well, development package and asset level which feeds into production and recovery forecasts, f) plan future optimisation studies or pilots and g) most importantly offers a consistent, efficient and compliant framework that can be applied across multiple assets, engineering teams and service providers. This paper focuses on capabilities and advantages of using a macro to automate stimulation design allocation for CSG multi-well (>100 wells) assets. Details of individual stimulation designs for Walloons Coal measures are mentioned in other publications ( Kirk-Burnnand et al., 2015 and Flottmann et al. 2018 ) and hence not covered here.

Bulk permeability of coal is a critical parameter in coalbed methane (CBM) or coal seam gas (CSG) well completion designs and field development planning. The estimation of permeability can be made by well testing either during drilling or production; however, well tests are costly, time sensitive and resource-intensive. Therefore, field-wide estimates are often dependent on production data history-matching, which has a high degree of uncertainty. In this paper, we present a new attempt to apply machine learning approach to estimate coal permeability using drilling data. We first extract important parameters from well test analyses, which are obtained using a packer element testing (PET) tool from four wells in the Surat Basin, Australia. Then drilling data from the wells are processed and fed into different artificial neural networks (ANNs), which include multi-layer perceptrons (MLP), convolutional neural network (CNN), and recurrent neural network (RNN). Two types of models are constructed: regression model with permeability values, and classification model with permeability class intervals (i.e., low, medium, and high permeability values). The evaluation metrics include R 2 for regression models and confusion matrix for classification models. Results show that the drilling mud losses are generally higher in coal layers and lower in interburden formations. The predicted medium and high coal permeabilities from MLP and CNN are in good agreement with measured permeability values from PET data. For the classification task, the CNN achieved an overall accuracy of 99%. Thus, an improved coal permeability map with a higher resolution and less calibration against PET data can be developed quickly to aid production data history matching. The developed machine learning model demonstrated a potential to be applied to new wells to predict the coal permeability for the Surat Basin as well as other CSG appraisal projects. This model can allow more rapid optimisation of well spacing, improved downhole pump design, more targeted well stimulation, and overall project economics.

A multi-chamber, finite-difference dynamic model assumed pore-scale reservoir properties and replicated laboratory processes to determine oil-water transition zone characteristics: (1) imbibition residual oil saturation to water flood (distributed as a function of rock properties); (2) imbibition oil-water relative permeability (according to both steady-state and unsteady-state calculations); and, (3) microscopic oil recovery factor as a function of height above free water level. A priori, scaled capillary pressure hysteresis and segregated flow conditions governed pore-scale flow behaviour (initial mobile saturation scaled 0-1) assuming a pipeline network analogue. Although an oil-water system was modelled the process could be extended to other fluid phases. The dynamic model was divided into five chambers replicating two experiments. Flow between chambers was regulated by transmissibility multipliers (open/shut). Replicating a core displacement experiment, an oil source rock "drained" (flooded) the central core chamber to form the oil-water transition zone; water then imbibed into the core chamber displacing mobile oil into a shallower effluent chamber; capillary pressure hysteresis defined the imbibition residual oil saturation to water flood. In a second experiment, the central core chamber was subdivided into zones, each comprising five model layers, and the imbibition oil-water relative permeability was determined by flooding the quiesced core chamber situated between high/low-pressure chambers (source/sink). Both steady-state and unsteady-state relative permeability were determined across the oil-water transition zone. The Digital Core Laboratory (DCL) determined the distribution of imbibition residual oil saturation as a function of: wettability assumption; rock properties; and, proximity to the free water level. For a range of wettability assumptions, imbibition oil-water relative permeability was determined across the transition zone, on a zonal basis, from top core chamber (top reservoir) down to the free water level. Summary of Results: (1) The imbibition residual oil saturation (ISorw) decreased with depth toward the free water level, while the drainage irreducible water saturation (Swir) increased with depth; (2) ISorw was found to be strongly influenced by the wettability assumption, contrasting with the uniformity of Swir; (3) Microscopic oil recovery factor was determined across the transition zone as a function of both proximity to the free water level and the wettability assumption; except for the oil-wet case, microscopic oil recovery factor increased with depth toward the free water level. The novel approach was the multi-chambered design of the finite difference model forming a Digital Core Laboratory (DCL). Tuning the model to a Special Core Analysis (SCAL) data set, with the objective of filling SCAL data gaps, is expected to be one application.

Based on three established commercial test cases, this paper documents their polymer flood process performance, revealing the impact of reservoir properties and heterogeneity on incremental recovery and dynamic performance. The key reservoir management measures for improving polymer flood sweeping efficiency are illustrated, which are particularly important for the successful application of chemical EOR techniques in heterogeneous sandstone reservoirs. The three cases produced oil with similar fluid properties from sandstone reservoirs. They all adopted 5-spot well patterns, which provide excellent examples for studying the impact of reservoir property and heterogeneity on incremental recovery. The producing reservoir sands in the three pilot represent two types. The former is of high permeability and low heterogenity. The latter is characterized by low permeability, multiple flow units, thin individual sand layers and high inter-layer permeability contrast. The authors reviewed and compared changes in water-cut and production rate performance versus pore volume of polymer solution injected during the process, as well as the applied well spacing, polymer utilization, and ultimate incremental recoveries. The two high quality reservoir cases adopted 22 ac well spacing, achieved an incremental recovery of 12.5% and 13.7%, a low polymer utilization of 1.08 kg/BO and 1.79 kg/BO, respectively, and a maximum water-cut reduction of 24.4%. In the low permeability case, although a much smaller well spacing of 11 ac was adopted, it achieved a relatively low incremental recovery of 8.2% and a maximum water-cut drop of 5.2%, with a polymer utilization of 2.51 kg/BO. Incremental EUR of individual producer through polymer flood is 49 MBO in the low permeability case, compared with 130 MBO in the high permeability reservoir sands. The three cases proved the effectiveness of fit-for-purpose reservoir management and conformance improvement techniques in improving polymer flood sweep efficiency to achieve high incremental recovery. Such techniques include hydraulic fracturing of low permeability sands, optimization of polymer solution concentration and molecular weight to adapt to different sand units with varied permeability, optimization of injection process to maintain a uniform pressure system, adjustment of injection direction to sweep by-passed remaining oil, and, zonal injection to improve polymer solution intake in low permeability sand units. The discussed cases proved the technical feasibility and economic viability of polymer flood in sandstone reservoirs with varied heterogeneities and revealed the impact of heterogeneity on performance and incremental recovery. The reservoir management and conformance improvement efforts during polymer flood process provided valuable lessons and best practices for similar applications.

The Jurassic Plover Formation is one of two reservoirs in the Ichthys Field, North West Shelf of Australia. It consists of fluvial to shallow-marine sandstones, shales and igneous rocks. The objective of this study is to build multiple scenario-based models to optimise development planning in preparation for the upcoming production phase. We have integrated data and interpretations of thin sections, cores, well logs and seismic data to create multiple geological concepts for the field and to identify key geological uncertainties. As the reservoir is geologically complex and many uncertainties were initially identified, it is essential to single out those uncertainties which have a significant impact on the development planning. We have established the key uncertainties and optimal model design for practical use through multi-disciplinary discussions and by running sensitivity models to check the production performance. A rock type (RT) scheme has been devised based on detailed petrographic observations and justified in terms of sedimentology and diagenesis. Using the scheme, a wide range of permeability variations in the sandstones has been captured and modelled. Environments of deposition (EOD) are firstly interpreted at core and well-log scales, then upscaled to the model zone scale. The EOD interpretations are laterally extended using lithology (sandstone, shale and igneous rock) probability maps derived from quantitative seismic interpretation (QSI). Multiple EOD scenarios are generated to capture the possible range of reservoir distributions. Each EOD is characterised by a unique net-sand porosity and RT proportion based on the well data. These values are used to define multiple possible porosity trends and RT proportions, guided by the EOD maps. The distribution and quality of the reservoir sandstones have been identified as key uncertainties. Another key uncertainty is reservoir compartmentalisation, thought to be mainly caused by sheet-like igneous intrusions. Subtle seismic lineaments are regarded as possible indications of such igneous intrusions, and multiple compartmentalisation scenarios have been prepared based on our understanding of igneous activity across the field. Reservoir structure and water saturation are also recognised as key uncertainties. Integrating the key uncertainties, we have established a practical modelling workflow and built multiple scenario-based models to cover a sufficient range of geological uncertainty. The workflow is also adaptive for future history matching, enabling us to flexibly edit the model properties under geological constraints. A decision tree for development planning, which defines a series of decisions for the well sequence depending on the well results, will be prepared based on the multiple scenario-based models delivered in this study. This will enable us to prepare for any potential decision-making in advance. The development planning will be continuously optimised throughout the production phase by simply selecting the scenario-based models most in line with the well results.

The Dvalin gas field is located in the Norwegian sea on NCS and is operated by Wintershall DEA Norge. It is supported by two independent reservoir structures, Dvalin East and Dvalin West. The field was explored through wells 14S and 15S in 2010 and 2012, respectively. The field is characterized by dry gas, high CO2, high temperature (160 °C) and high pressure (SIWHP 620 bar). The targeted Garn sandstone has good reservoir quality, but with a high permeability contrast. The field development was sanctioned in 2016 and calls for a 4 well solution through a centrally located subsea template, producing gas back to the host platform Heidrun TLP 15 km away. Water depth at location is 380 m and targeted reservoirs are at 4140 m MSL (East) and 4240 m MSL (West). Production plateau rates are estimated to be approximately 106 MMscf/D (3 million std m 3 /d) per well where thin high-permeability zones within the Garn formation are expected to dominate the inflow. The lateral facies development is thought to be relatively homogenous throughout the field, thus S-shape wells falling off to vertical through the reservoir will ensure effective drainage. Sand failure is expected after short time of production and would increase the risk of erosion causing severe damage to well jewelry and production facilities. It has been decided to integrate sand screens as a means of downhole sand control as part of the primary lower completion design. The sand screens will offer sand control, erosion resistance, hot spotting resistance as well as robustness towards a full hole collapse during reservoir pressure depletion. As the subsea completions are carried out from a mobile drilling unit in harsh environments, protection of the sand control filter media during installation is of utmost importance. This paper will describe the selection process of sand control and qualification steps carried out to use ceramic screens as the stand-alone screen solution for successful deployment and integrity for the Dvalin field development

This paper describes the extensive integrated engineering collaboration and optimization process to allow the operator to push the drilling and completion envelope to drill complex ultra extended reach drilling (ERD) wells in a mature field. The Wandoo field is located within WA-14L in the Carnarvon Basin, offshore Western Australia and is wholly owned and operated by Vermilion Oil & Gas Australia Pty Ltd (VOGA). Due to the shallow reservoir depth, extreme ERD profile and the high tortuosity requirement for the wells, significant challenges were identified during the planning stages of the campaign. To optimize well placement, update geological information and reduce collision risk with nearby producing wells, the Reservoir Mapping While Drilling (RMWD) service was run in real-time. The primary objective of the service was to place the well in the optimum position within the reservoir, this included (1) provide early detection of moved oil water contact (MOWC) while approaching well crossings with minimum separation factor to reduce collision risk and geological uncertainties; (2) to steer azimuthally to optimize the placement of the well with respect to the field bounding fault and reduce the drilling risk associated with the intersection of the fault; and (3) to distinguish between the A3 Upper (A3U), A3 Lower (A3L), and B sands to optimize well placement. These challenges were successfully overcome with extensive planning, integrated engineering designs, application of new state-of-the-art technology, good quality real-time data interpretation and a strong execution support from both rig site and town. As the result of good collaborative teamwork in planning and execution, the two highly technically challenging wells were drilled and completed successfully and brought online for production. A number of drilling performance highlights captured during the execution phase were identified as having significantly contributed to the successful completion of the project.

Formation evaluation including porosity and directional permeability assessment in complex carbonate formations is challenging due to the anisotropic and heterogeneous nature of the formation. The pore structure can be captured by digital rock technology, which makes the constriction of numerical whole core, and the numerical simulations of chemical enhanced oil recovery on digital rock possible. We introduce a new workflow to construct the digital rock based on micron-CT scanned sequential images of the carbonate sample. Firstly, we apply the modified Otsu's global thresholding method to convert the grey-scale micron-CT scanned images to binary images, and we systematically divide the whole core 3D segmented image into small blocks or representative elementary volume (totally 10143 blocks including inactive blocks). Then we estimate the porosity of each block, and use Lattice Boltzmann Method (LBM) to simulate fluid flow in randomly selected blocks and accurately compute the directional permeability of these blocks by simulating Darcy flow through them. The permeability tensor of other blocks is estimated by applying Kriging method based on the estimated porosity of all the blocks and the accurately calculated permeability tensor of the selected blocks. Then we simulate the polymer flooding on the constructed digital rock and show that the simulation process is computational efficient. We calculate the porosity and permeability of the constructed digital whole core and compare them with laboratory measurements. The image analyzed porosity of whole digital rock is comparable with laboratory measurements by only 1% difference. The simulated permeability value with calibration of the whole digital rock is also in good agreement with experimental result by 3.5% difference. Then we simulate the polymer flooding on the constructed digital rock and show that the simulation process is computational efficient. The proposed digital whole core construction workflow integrates the accuracy of LBM simulation and the efficiency of kriging method. The accurately constructed digital whole core only have 10143 blocks including inactive blocks, which greatly reduces the heavy computation time of chemical enhanced oil recovery simulation on digital rock and makes the proposed method more practical in routine analysis and modeling.

Neutral wet proppant plays a pivotal role in maximizing the flow back of fracturing fluids and the recovery of produced hydrocarbons. An accurate and repeatable contact angle measurements are extremely challenging because of proppant spherical shape and small size. This paper presents a methodology of direct contact angle measurements in spherical particles examined with high strength coated ceramic proppant. 20/40 and 25 HSP non coated proppants were used for the study. Coating material was applied to the proppant sample to obtain non-wetting characteristics. KRUSS Drop shape Analyzer was utilized to measure the contact angle using a modified pendent drop method. Step by step procedure is detailed and possible sources of errors were identified, and recommendations were introduced accordingly. HSP coated proppant showed contact angle measurements of 117-120° and 84-114° with deionized water and hydrocarbon samples, respectively. Ideally, a neutrally wetted surface would have a contact angle of 90°. This indicates that the proppant is neutral to slightly oil-wet. Wetting characteristics are dependent of hydrocarbon type. For instance, Condensate 2 have a contact angle of 102.3° indicating neutral wetting characteristics, whereas Condensate 3 shows contact angle of 84.5° indicating slightly oil-wet character. Geometry of hydrocarbon droplets modified the adhesion tension of oil, nevertheless had insignificant effect with water drops. For example, tripling the droplet size of Condensate 2 and Diesel resulted in increment in contact angle values of 12° and 15°, respectively.

In CO 2 storage projects, CO 2 usually enters the target reservoir at a lower temperature than that of the surrounding rock and its density is increased. The injection temperature affects how much CO 2 can be stored. In this work we investigate the impact of heat exchange during CO 2 injection into the Surat Basin, Australia, using integrated reservoir modelling. We evaluate the aquifer storage and sealing capacities, as well as pressure build up and CO 2 plume migration. Flow simulations of CO 2 injection into the Precipice Sandstone were conducted with injection temperature from 40 to 80°C. The modelling domain consists of the reservoir sandstone, an overlying transition zone (muddy sandstone) and above it, the ultimate seal. The distribution of porosity, permeability and capillary pressure is heterogeneous. Heat exchange between rock and fluids was enabled in the commercial simulator to evaluate changes in fluid properties due to wellbore cooling. The initial temperature was set to 80°C. The injector’s wellbore pressure drop is modelled honouring a constant well head pressure of 15,000 kPa. The maximum allowed bottom-hole pressure is 90% of a thermally reduced fracturing pressure. The viscosity of water and CO 2 increases during cooling of the near wellbore zone; thus, pressure build up grows faster in the case of lower injection temperatures. Although the bottom-hole pressure becomes higher, injection rate is constrained by well head pressure. Heat exchange also increases the density and saturation of CO 2 at the plume edge, which causes a sharper and faster advancing front. Higher pressure in the reservoir forces fluids to migrate to the transition zone, which also reduces its temperature. CO 2 flows preferentially through the lowest capillary pressure channels and is able to permeate slightly into the transition zone. These physical conditions at the bottom of the well (lower temperature and higher pressure) lead to a denser CO 2 plume and a greater mass is stored in the reservoir each year. This work analyses non-isothermal injection of CO 2 into an aquifer using integrated reservoir modelling. It illustrates how reservoir cooling may increase the rate of CO 2 storage and slight migration to the transition zone.