In 2014 ConocoPhillips (CoP) decided to focus on the Jet-type perforate, wash and cement (P/W/C) technique as its primary permanent well abandonment method for setting a full cross-sectional cement/steel barrier. Following this decision, a quality improvement project was launched to prepare for a transition from Cup-type to Jet-type P/W/C to improve barrier plug quality. The initiative was presented during the Stavanger P&A Forum (PAF) conference October 2014 for information and to indicate for specific vendors that there were opportunities for participation. The perforate, wash and cement method is complex and as with any cementing operation there is operational risk involved. This paper is written to share ConocoPhillips experience and learning from the improvement project which is still ongoing. It is specifically written for drilling engineers planning Jet-type P/W/C operation to help identifying key parameters to achieve a top-quality operation as well as managing the operational risk inherent to the operation. Quality requirement in P&A operations? It can be a hard sell to argue for costly fluids, BHAs (bottom hole assembly) and TCP (tubing conveyed perforation) guns to plug off a depleted reservoir where the test of time is hundreds of years from now as the reservoir gets pressurized again. The latter is not the case in the Greater Ekofisk Area (GEA) where active water injection increases the average reservoir pressure quickly and the established production strategy is dependent on good isolation of abandoned wellbores. To get a ‘’good’’ P&A plug you need to understand how to prioritize and control the variables such as cement properties, drilling fluid properties, drill pipe and BHA design, hole cleaning, ECD, displacement, TCP performance, operational sequence and many more. ConocoPhillips have made a structured approach to build a process which captures the basics of getting a high quality well abandonment plug. The displacement process itself has been modelled with computational fluids dynamics (CFD) software to understand key drivers for the placement of a cross-sectional P&A plug. This understanding has been mated with the practical limitations from a standard drilling unit to get a robust operational plan. To ensure the quality is maintained from operation to operation, the process have been accurately described in a Best Practice document. The operation itself is checked against a QA form to verify that execution was performed according to plan. The QA form is then filed as part of the P&A documentation, similar as a casing test during well construction. In the GEA experience a good P/W/C P&A plug is one set as per the Best Practice document where the operation is quality assured with an "all green" QA (quality assurance) sheet. A more tangible description is offered: After the operation the offshore cement sample which is contaminated with 10% mud will set up in the UCA (ultrasonic cement analyser) cell per programmed setting time plus no more than 3 hrs. The cement plug itself will be tagged at planned TOC (top of cement) +/- 20 ft. It will hold the positive pressure test to fracture gradient + 1000 psi. From time to time the plug will be drilled out. If that is the case, we expect to see an average weight on bit larger than 15,000 lbs for a 9 5/8’’ casing plug. The external well barrier element may be logged using a CBL/USIT (cement bond log) string or similar. In that event we expect to see "bond quality", which is a weighted interpretation of CBL, VDL (variable density log), flexural attenuation and pulse echo measurements as "good" to "very good" throughout the perforated section. This paper is one of many discussing the P/W/C technique (1) and is written to help you prioritize focus areas and optimize those. We think a high focus on QA will be your fundament, not only for a "good" P&A plug but also for a flawless execution of the complex offshore operation. Our results can be reviewed in Appendix B . Performance approach technical limit.

As for the thick salt-gypsum formation and the target strata in the Kuqa piedmont zone of Tarim basin in western China, The biggest challenge in well cementing is the narrow safety density window (only 0 g/cm 3 -0.1 g/cm 3 or 0ppg-0.833ppg) and the unsatisfactory leakage blocking technology under pressure (the improvement of formation pressure-bearing capacity is less than 0.1 g/cm3 or 0.833ppg). The limited flow rates (0.6m/s-1m/s lost still) during cementing operation are distinctly insufficient for displacement efficiency. In response to this challenge, a numerical simulation study has been carried out using the computational fluid dynamics (CFD) software ANSYA Fluent to explore practical guidelines in these formations. The models we build are annulus with a 176.7mm (6 5/8 " bit expanding 5%) outer diameter for the hole and a 139.7mm(5 1/2") inner diameter for the casing, the length is 11 meters or 22 meters, and the eccentricities are 0.3, which means a sufficient centralizer according to our practical experience. The 11-meter and 22-meter models have one million and two million grids, respectively. In the thin boundary layer area four thin boundary layers were constructed. The species model and the viscous laminar model have been applied, and the velocity inlet and the outflow outlet have been set as the boundary conditions. Both the mud, the spacer and the cement slurry are non-Newtonian Herschel-Buckley(H-B) fluids, whose rheological properties are determined by the flow index n, consistency coefficient K and yield point YP. By analyzing the interface characteristics of the mixing slurry, distribution of mud mass fraction and wall shear stress at different inlet velocity and displacing time during the displacement process, the effects on the displacement efficiency for each individual factor, such as casing centralizer, flow rate, and rheological properties, have been analyzed and summarized. According to these simulations, a series of guidelines have been drawn. A sufficient casing centralization is the most important approach to improve the displacement efficiency. Flow rate and wall shear stress also play an important role, but they are limited by the safety density windows of the formations. Under the circumstances, the most practical way to improve the displacement efficiency is to optimize the rheological parameters of the mud-spacer-cement slurry (for instance, to decrease the consistency coefficient K and yield point YP of the spacer) to achieve a larger friction gradient difference and get a better displacement efficiency eventually. These guidelines, which have been applied in the X-well of Kuqa piedmont, have shown a remarkable achievement in cement sheath evaluation across the primary zone of interest (qualification rate improved from an average 49% to 80.3%), and therefore are practical in the formations with narrow safety density window.

Cement behind casing, as the critical component of well integrity is a real challenge all over the world. Despite the efforts drilling operators and service providers dedicate to this phase of well construction in the South Pars gas field, final set cement quality does not establish zonal isolation in 9 5/8" casing and 12 1/4" openhole section. In order to study this issue, twenty-four wells have been analyzed based on theoretical analysis, close hands-on operations and track record of cementing in the field. Data were acquired from the daily drilling reports, data acquisition system of cement units, mud logging records, daily mud reports, cement slurry laboratory test sheets and wireline log records. The main effective factors on cement quality have been studied in four groups namely: well preparation, slurry design, mud removal and post-cementing practices. Good and poor quality cement in all wells have been compared with actual field parameters using a cementing displacement simulator software. Structural stress model has also performed for one of the wells whose cement was prone to be impacted by post cementing practices. Results have been obtained over one year of parallel laboratory testing, field experience, simulation and evaluation. The simulations results illustrate turbulent flow is not practical for cementing of this section and effective laminar flow technique shows an efficient alternative, however all criteria of this technique could not have been fully met due to some well restriction. The results reveal mud removal parameters in terms of casing centralization have significant effects on the final cement quality in this field. Cement quality devastation persisted even in cases where the cement slurry properties were modified and used in four wells in order to evaluate slurry design impact degree on final set cement quality. The stress model results illustrate that imposed stress on the well exceeds the compressive and tensile strength of the cement sheath. These results reinforce the idea that mud removal and post cementing practices govern the cement quality in the field. This paper is a comprehensive study of all effective parameters on cement quality in 9 5/8" casing cementing and highlight the main sources of cement quality devastation in the field and it can be used as a guideline for cementing similar cases around the world.

Design, execution, and evaluation of cement operations using a new liquid-bead cement system helped achieve the necessary top of cement for development wells in Brunei. Glass beads are a common lightweight material used within the oil industry to generate low-density slurry designs with competent compressive strength development. For Brunei offshore operations, using dry beads poses many challenges, such as rig silo management, quality control of blends, and waste. A new approach has been proposed using a liquid-bead system to produce lightweight cement slurries by adding beads stabilized within a fluid as another liquid additive to help reduce the need for dry bulk blending of beads. Planning, execution, and post-operation evaluation methods were developed for this new approach. The liquid beads can be added to cement slurries using liquid additive pumps. For Brunei's operation, a mobile injection skid was developed to inject liquid beads at a predetermined rate into the suction header of the cement unit triplex pump while the base slurry is being mixed and pumped at a predetermined rate on the fly. Extensive laboratory tests were performed on the liquid slurry and the final set product to demonstrate the liquid-bead influence on cement properties compared to a dry-blend bead design. To validate this technology, a field mixing trial was performed at the rigsite. Cement evaluation with conventional logging tools poses an additional challenge for beaded slurries. To evaluate cement placement, a bond log post-process analysis was performed. The first Brunei offshore trial operation, executed during April 2018, was a 9 5/8-in. production casing where 13 m 3 of a liquid-bead cement slurry design was mixed, pumped, and successfully placed within the annulus. Laboratory testing validations and injection skid and post-operation cement evaluations are discussed.

The Australian coal seam gas (CSG)/coal bed methane (CBM) fields present multiple challenges (i.e., losses, naturally fractured formations, and highly depleted zones) typically addressed using various well design and cementing techniques (i.e., additional casing strings, stage cementers/tools, lost-circulation materials, lightweight designs, and additional cement volume) to manage the potential risk of losses. Foamed cement is a viable option to address these challenges; however, despite the documented benefits, its application within Australia has been minimal at best. The lack of application can be primarily attributed to misconceptions concerning cost, potential risk, excessive equipment footprint, and a limited proven track record, which increases the potential risk of execution. A recent 10-well campaign conducted within the Bowen Basin, Queensland, Australia, demonstrated that foamed cement can be used as an alternative to traditional lightweight and/or elastomeric cement slurries. Further, the benefits of foamed cement make it an economically and technically advantageous solution compared to conventional cementing techniques used to overcome CSG challenges. This case study details the campaign challenges, cement design, and detailed results of the 10 wells with the intention of providing other engineers a road map to better understand foamed cementing with a specific Australian context and how it could be applied to their projects.

The main purposes of employing cement in oil wells are to isolate the zones within formations, secure casing from axial loading and corrosion and improve wellbore integrity. There are plenty of nanomaterials represented in the literature which were introduced to cement in order to advance the strength and rheological properties of cement slurry. The objective of this study is to propose a novel nanomaterial which can upgrade the mechanical and rheological properties of cement. The smaller the size of Nano-particles, the higher surface area and hence higher efficiency they possess to advance particular properties of the support material. Bio-templating has been offered as an approach to reduce the size of utilized nanoparticles. In this study, Nanosilica particles were synthesized and functionalized using modified sol-gel method. Bio-templating was then implemented through crosslinking of the procured Nanosilica with soluble egg protein using glutaraldehyde. In order to investigate the effect of bio-templated Nanosilica on cement slurry, synthesized Nanosilica was added to cement and rheological and mechanical experiments were conducted. To validate the performed bio-templating, ATR-FTIR spectrum was acquired which confirmed successful crosslinking between the functionalized Nanosilica and SEP. Furthermore, experimental tests were conducted to evaluate the effect of bio-templated Nanosilica on mechanical and rheological properties of neat cement. The results were then compared to inclusion of commercial Nanosilica in cement. Through the rheological studies, it was found that the modified Nanosilica has acted as dispersant in cementitious system by decreasing the plastic viscosity of cement and maintaining the density. It was also obtained that novel bio-templated Nanosilica has significantly increased uniaxial compressive strength of cementitious system by 16.59% upon addition of only 0.25 wt.%. It was due to its pozzolanic reaction in cement and its pore filling effect where the porosity of cementitious system was decreased. The proposed synthesized Nanosilica demonstrates superior results than commercial Nanosilica which shows its remarkable efficiency in cement strength reinforcement and rheological properties improvement. The research study has successfully proposed a novel method to utilize biomaterial waste in the process of synthesizing Nanosilica particles which is not only environmental friendly but also yields in phenomenal rheological and mechanical properties of Class G cement.

The development of Early Permian reservoirs in the Fairview Field is limited by highly depleted shallower Bandanna coal seams and naturally fractured formations that would not allow to reach the original geological goals. Offset wells in the area had been executed as three string well design due to long open hole section across depleted Bandanna and multiple loss zones. Multi-stage cementing was required to ensure there is proper zonal isolation. These resulted in significant incremental cost to achieve 5-1/2″ production casing. Through the depletion of upper coals, fracture pressure in these zones has decreased due to reduction in pore pressure. Drilling in two string design carries higher execution risk due to long open hole section, depleted formations and differential sticking, highly fractured formations, narrow window between fracture gradient and pore pressure, and multiple loss zones which demands special techniques for treatment of loss zones and hole stabilisation while drilling. Considering the downhole conditions, which pore pressure ranging from 2 to 9 ppg in the different formations, the importance of zonal isolation, establishing barriers in aquifers and achieving overall cement coverage is also extremely important. With introduction of various new LCM products, cement plugs, foam cementing, RCD for drilling with no returns (blind drilling), Santos has achieved major success developing Early Permian fields. This Paper describes how two string design was successfully implemented to drill Early Permian wells. This paper serves as an operational guide to ensure challenging depleted and highly fractured zones can be successfully drilled while minimising risks.

The Vostochno-Messoyakhskoe field is the northernmost active continental field in the Russian Federation ( Fig. 1 ). This field is located 250 km from the Arctic Circle, in the arctic climatic zone. Full production drilling only began in 2015 because of the field's geological complexity and lack of transportation structure. Weather conditions, such as strong winds and extremely low temperatures, can be hazardous to personnel and equipment. Additionally, this oil field has permafrost zones (400m from the surface) and low formation temperatures at the production zone. Also, because of permafrost zones, there is a high risk of thawing the wellhead formation. These conditions significantly affect which technologies can be applied during drilling and completion of the wells. Therefore, special cement designs are necessary to help reduce risks associated with low temperatures and permafrost zones in the Vostochno-Messoyakhskoe field. Production is further complicated by a gas layer at 720 to 820m true vertical depth (TVD) and high formation pore pressure. This can make the cement operations with the production casings difficult. While the TVD of the casing landing is not relatively deep, the measured depth (MD) in extended reach drilling (ERD) wells is significant ( Fig. 2 ). ERD wells can challenge cement displacement efficiency ( Sabins, 1990 ). Mud removal efficiency may not be enough to create a high-quality cement barrier and isolate formations from gas migration. Poor mud removal can affect future life of the wells and crude oil production. To perform remedial jobs, it is necessary to stop production for several days. Due to experience in performing remedial jobs in the Messoyakhskoe field, it is usually necessary to perform a few attempts of the remedial cementing operation to reach positive results. Therefore, the operator decided to utilize hydraulic packers to create a second barrier between the surface and production casings to help prevent gas migration to the surface, save time associated with remedial operations, and extend the life of future wells.

Expansion additives have been used in cement plugs to mitigate the potential risk of plug failure resulting from shrinkage. These additives are effective only when their amount is tailored for downhole boundary conditions, and their role should be well understood. This work discusses using an improved testing method that enhances the dependability of the volume change measurement and exhibits the impact of test boundary conditions on the shrinking and expanding behaviors of cement plugs. Boundary conditions investigated with this method include temperature, pressure, water access to the cement from the formation, and the role of mechanical constraints. Dependability is demonstrated by verifying the repeatability and reproducibility of the method at two different laboratories. Together with the noninvasive continuous volume change, supplementary measurements, such as ultrasonic compressive strength, tensile strength, and chemical composition analysis, have provided inferences about the mechanism of volume change. The new method embodies all attributes listed in API 10 TR2 (1997) , including a constant external stress state in all measurements and a constant pore pressure during total volume change measurement. The results of percentage volume change from this test method present an extremely small variance, highlighting its repeatability; additionally, the measurement was reproducible between laboratories. Expansion value increased with a decrease in confining pressure, and excessive expansion in the absence of an effective confining pressure produced weak samples. The absence of outside water caused cement containing the expansion aid to shrink more than its neat equivalent; such observations highlight the importance of fluid boundary on the action of expansion additives. These observations were possible because the test method can capture temporal and boundary condition effects more aptly. Thus, the improved method provides a dependable measurement for tailoring plug properties.

A lightweight cement solution was successfully applied in deepwater wells at depths greater than 1000 m and in production liners terminating in depleted reservoirs. These wells were drilled off the east coast of India. The fracture gradient prognosis for the depleted zones ranged from 11.0 to 11.28 lbm/gal. The measured depth (MD) of these wells was more than 4500 m (MDRT). Mud weights ranged from 10.9 to 11 lbm/gal in the well while drilling the zone. The length of the liner normally ranged from 1400 to 2300 m. The cement slurry was finalized after conducting numerous tests in the laboratory. A lead and tail combination was used for the job to maintain the required equivalent circulating density (ECD). In openhole completions, the casing or liner before the gravel pack should be landed in sand to establish having reached the reservoir top and to help ensure that no shale is present. Challenges for a successful liner job in these wells include landing in a depleted reservoir, which would enable a very low margin between the mud weight and fracture gradient. This margin is further reduced by the minimum horizontal stress mud weight requirement to help ensure that no hole collapse occurs while drilling and before cementing begins. In addition to the depleted zone, to maximize reservoir tapping, the well profiles are highly deviated, often reaching a well deviation of 80+ degrees, resulting in a high ECD during cementing. A long section of the cement column can create problems of cement channeling past the mud and mixing in the annulus. The correct prediction of pore pressure and fracture pressure for different sections is very important. Accurate knowledge of these values is recommended for a correct job design. Some of the lessons learned during the process to help ensure good zonal isolation include the following: An 11-lbm/gal lightweight lead slurry was formulated, keeping ECD and fluid rheology vs. strength development in mind. Solids loading was controlled to help ensure low friction factors (considering rheology) and to achieve a final compressive strength of 2,000 psi because it was a production casing. The length of the tail slurry column was maintained to a minimum to create minimal effect on the ECD, even though the hydrostatic pressure developed was marginal in a highly deviated section. A low-rheology/low-density synthetic oil-based mud (SOBM) (10 lbm/gal) was pumped ahead to reduce the ECD and to maintain the equivalent static density (ESD) above the pore pressure. In addition, the displacement rate was staggered to help maintain the ECDs. A high-viscosity pill was spotted at the 12 1/4-in. section total depth (TD) before the final pullout to act as a base for the cement slurry. This paper highlights the concerns and best practices developed when cementing production liners across depleted formations in deepwater wells.

Oil and gas well integrity is obtained by placing a steel casing in the well and a cement sheath in the resulting casing/formation annulus. To provide zonal isolation, a large portfolio of cementing technology is available to meet various well conditions. Some of these technologies involve dry-blending operations and cement-blend handling of specific-tuned-blends mixing together particles of different characteristics in terms of density, shape, size, and chemistry including mineral and/or organic components. These blends are usually transported pneumatically and loaded to the rig then transferred to the rig silos. During the different transfers, the blend may be prone to segregation, thereby losing its homogeneity, which makes it difficult to use or even unusable. Flowability is an important blend property for the blend-handling process. Segregation can be viewed as a mechanism leading to a nonrandom degree of uniformity of the different blend components at the scale at which end-use properties are required. Overall, the differences between particles in chemical nature, density, size, and shape will influence the flowability and, above all, the tendency to segregate. Dealing with blends is, therefore complex since they contain small, medium, and coarse particles in various proportions depending on the targeted slurry density and set material properties. To counter this challenge, an innovative methodology and equipment to characterize the blend flowability and robustness to segregation were developed and implemented. The laboratory results were validated with those obtained in the large-scale results using a pneumatic conveying flow-loop. The implementation of the new methodology during the design phase of the cement job was used as a preventive measure to validate the design and quality control of the blend before the blend is prepared and sent to the rig. This helped in designing robust homogeneous blends and reducing the likelihood of blend transfer problems, thus ensuring the placement of the right quality cement slurry and assuring downhole well integrity. The new methodology described in this paper was applied to tune several field blends known or identified to have problems and to develop of new generation of cementing technologies. The outcome of this multidisciplinary approach of blend characterization helps the oil and gas industry to anticipate blend-handling issues and to continuously improve quality and field handling of engineered complex blends with high confidence and consistency.

Sustained casing pressure (SCP) is a major risk encountered in most wells in India, particularly in developmental oil and gas fields situated in the northwest area of the country. The inability of conventional cement systems to withstand cumulative stresses from completion and production phases might be one of the primary reasons for the failure of expected barriers during zonal isolation, which can lead to SCP. This case study reviews a flexible cement system used in an oil and gas field located in northwestern India, including extensive laboratory evaluation, operational design, execution, and well evaluation. The field requirement was to design a gas-tight, lightweight slurry for a production zone to treat losses and address issues of SCP. A finite element analysis (FEA) structural simulation was performed, which modeled the lifetime operation of the well. Including elastomeric and tensile strength enhancement materials in the cement system was recommended based on results from structural simulation to reduce risks of SCP. Incorporating these materials can enhance a cement system's mechanical properties (i.e., increase Poisson's ratio and tensile strength and decrease Young's modulus). The slurry was designed with cement, hollow spheres, lost circulation material (LCM), a tensile strength enhancer, and elastomeric material; the cement slurry was batch mixed to ensure homogeneity. The case study examines the impact of the fluid rheological hierarchy, pump rates, and multiple bottom plugs on cement slurry displacement efficiency using computational fluid dynamics (CFD). A finite-difference, three-dimensional (3D) displacement simulator was used to predict the flow behavior of fluids, both inside and outside the casing, throughout the operation using actual operational parameters. Based on two-dimensional (2D) hydraulics analysis, various factors, including rheology, pumping rates, and fluid density, were adjusted to maintain equivalent circulating densities (ECDs) below the fracture pressure to help avoid losses. A tailored cement design, which created a stable gas-tight resilient cement system, helped minimize risks to production by achieving effective zonal isolation. This was confirmed through a post-operation review. The cement bond log, including a microseismogram and circumferential visualization, indicated that the cement was adequately placed around the casing. The increase in the cement system tensile strength helped ensure wellbore integrity, even in high-stress/strain load cycle production environments. Cementing operation success was confirmed by excellent cement bond logs and zero SCP observed between the production and surface well casing annulus. The life-of-the-well tool is an engineered, proactive, and interventionless zonal isolation solution to help extend well economic life, thus preserving production while reducing or even eliminating costly remediation ( Ravi et al. 2002 ).

During primary cementing of coalbed methane (CBM) wells, it is necessary to consider slurry designs not typically encountered during conventional cementing operations. An important difference between coal seams and conventional reservoirs is the cleat system of coal. This unique petrophysical property of coal should be factored into the design to meet the basic tenets of primary cementing (i.e., zonal isolation and casing support). This paper presents cement design considerations, case histories, and best practices developed during the course of seven years of cementing operations in CBM wells in India. It also presents the cement bond evaluations that verify the conclusions. Formation damage, lost circulation, low-fracture gradients, shallow gas, and coal seam gas are the most frequent challenges encountered during cementation of CBM wells. Cement and cement filtrate loss can plug the cleat matrix and cause reduced well productivity, increased injection pressures, and ineffective stimulation operations. These challenges are exacerbated by the necessity for long cement columns that cover multiple coal seams. Cement operations must also provide excellent annular displacement efficiency to achieve the necessary annular fill and provide zonal isolation during the life of the well. Adequate compressive-strength development can be difficult to achieve in low-temperature CBM environments. Selection of cement and additives necessary for slurry design are governed by the ability to meet the operator's objectives at temperatures ranging from 45 to 80°C. The thixotropic properties engineered into the cement slurry help enable rapid gel-strength development once the slurry column is placed. This helps remediate lost circulation, reduce cement contamination into the coal cleat system, and reduce fallback. Best operational practices for preparing the wellbore for effective cementing, such as optimum flow rate, hole conditioning, and centralization, help ensure complete isolation of coal intervals with cost synergies achieved through efficient deliverance preparedness. A three-dimensional (3D) displacement simulator models the intermixing of wellbore fluids and corresponding changes in rheology. This simulator, which contains a built-in, free-fall algorithm, helps provide a more accurate estimation of fluid movement/flow patterns. It also simulates intermixing of fluids, which helps better predict equivalent circulating densities (ECDs) and frictional pressures. The 3D displacement simulation results and their agreement with cement bond log (CBL) evaluations help verify the effectiveness of controlling critical operational parameters and their effect on cement displacement efficiency. The combination of high-strength, low-density (HSLD) cement slurry, efficient field-blending procedures, and operational considerations helped enable successful cement operations in 200 CBM wells in the Sohagpur-West block, Madhya Pradesh. The unique advantages of the HSLD cement slurries include Reduced density, which helps prevent formation damage and lost circulation High compressive strength Gas-tight properties that help prevent annular gas migration Eliminating the need for stage cementing

Cementing across highly depleted zones and weaker formations requires low density cement systems capable of reducing the hydrostatic pressure of the fluid column during cement placement. If wellbores encounter weak or depleted zones, standard cement cannot be used because the bottom-hole pressure will exceed the pressure gradient and cement will be lost to the formation. Service companies offer cement solutions made light enough to circulate in such situations while retaining the ability to withstand down-hole conditions and maintaining adequate compressive strength to meet regulatory guidelines. Lightweight cements can be achieved using water extension, foamed cement or lightweight microspheres. This paper focuses on the use of lightweight microspheres as density reducing agents. Preliminary experimental data comparing different grades of hollow microspheres is discussed. Cement slurries containing hollow glass spheres and other lightweight hollow microspheres were evaluated while still liquid and after cured. While still liquid the cement slurries were characterized in terms of effective density as a function of pressure. After being cured at room conditions, the resulting cement specimens were characterized in terms of compressive strength. Experimental data suggests that cement compressive strength is mostly independent of the lightweight microsphere strength and strongly dependent on the cement load. Guidelines on the selection of the appropriate microsphere grade are also presented.

Seguni field and Sejadi field are smaller regions of Sepinggan field in offshore of East Kalimantan, Indonesia, which were drilled and developed by the operator since 1977. Seguni-V (redrilled well) was prognosed to encounter several depleted sandstone formations with reduced pore pressure due to produced hydrocarbons. Consequently, the utilized drilling fluid density was set as low as reasonably practical and this methodology had successfully prevented any lost circulation event until the total depth (TD) was reached. Nonetheless, the risk of losses were greater in the cementation phase of the 3 1/2-in tubing due to long column of cement (>7000 ftMD) required. Therefore, the challenge was to reduce the cement slurry density that still can achieve a required compressive strength within timely manner. The reduced slurry density was also predicted to be instable downhole due to the immense bottomhole pressure, which might crush the conventional cenospheres in the slurry as lightweight materials and result in an increase of downhole slurry density. Therefore, to minimize the risk of induced lost circulation caused by slurry density increase, a novel lightweight material with highly-crush resistant property was proposed. The result of the job with this cement system was satisfactory with no losses occurred and the targeted intervals were covered with good cement. Sejadi field, on the other hand, had experienced losses while drilling, from seepage losses which were commonly found, up to 170 bbl/hr of loss rate at one of the wells in the field. A particular lost circulation case with persistent loss rate into depleted formations was observed at Sejadi-X well. 728 bbl of synthetic based mud (SBM) had been lost into the hole when a loss rate of >40 bbl/hr was encountered while drilling 8 1/2-in open hole (OH) section. The loss rate could not be reduced even after spotting three times of 30 bbl conventional lost circulation material (LCM) pill and had cost significant volume of SBM and LCM amount lost to the formation, as well as 2 rig days spent in attempt to cure the loss. The study of the previous failure on similar problems in the neighboring well led to the solution proposal to use engineered, optimized fiber in cement slurry for lost circulation plug. The result was prominently effective and drilling operation could be resumed to total depth. This paper describes the features, case histories, challenges, field applications, as well as the acknowledged results of mentioned technologies. Lastly, this paper also introduces a mutualistic technical feature when the two technologies are combined to both prevent and mitigate lost circulation.

Disclaimer: This paper includes forward-looking statements, Actual future conditions... The publication of the API Standard 65-2 "Isolating Potential Flow Zones During Well Construction" places strong emphasis on measuring the Critical Gel Strength Period (CGSP). The CGSP is the time period starting from when laboratory measurements indicate the slurry has developed Critical Static Gel Strength (CSGS), to when it has developed strength of 500 lbf/100ft2. As per the API standard, CGSP of 45 minutes or less has proven effective in isolating zones with severe flow potential therefore, the CGSP has been identified as a crucial parameter to qualify slurry systems for many oil and gas operators. The API 10B-6 "Recommended Practice on Determining the Static Gel Strength of Cement Formulations" indicates there are three measurement methods; continuous rotation, intermittent rotation, and ultrasonic-type static gel strength. This paper will review a comparative laboratory- based study between two measurement devices commonly used in the industry to measure the CGSP. One device uses the intermittent rotation, and the other uses the ultrasonic method. The slurry systems selected for the study covers a density range of 11.5 to 18 lbm/galUS within the temperature range of 27 to 121 deg C. The selected slurries comprise of Class G cement, silica flour with extenders or weighting agents paired with antifoam, fluid loss additives, dispersant and retarder to represent the typical slurry systems used in cementation of potential flow zones. Additionally, each slurry system is designed for two scenarios; one is to cover a short placement time(3 to 4 hours) and the other for a longer placement time (7 to 8 hours). While some of the slurry systems passed the CGSP criteria based on the ultrasonic method of measurement, they did not pass the criteria when measured by the intermittent rotation method. Possible reasons for this mismatch are further explained in this paper. Results of this study are applicable to all oil and gas service operators involved in cementation of potential flow zones. One would expect that both of these methods would predict the same slurry behavior in either passing or failing the CGSP criteria, however and on the contrary that was not observed on all of the slurry systems selected for this study.

Portland cement has become the prime material used for zonal isolation; sealing annuli between casings, between casing and formation and finally for plug and abandonment (P&A) operations. However, there are concerns regarding Portland cement such as autogenous shrinkage, high permeability after cracks has occurred, gas influx during waiting on cement (WOC) time, instability at high temperature, ductility and durability. Geopolymers have been suggested as an alternative to Portland cement for oil well applications. Geopolymers are inorganic aluminosilicate cementitious materials condensed as result of a complex reaction known as geopolymerization. The current work presents the usability of a geopolymeric material specially designed for oil well cementing applications, known as aplite rock-based geopolymer. The chemical reaction of the geopolymeric slurries was determined using calorimetry measurements. The rheological behavior of the geopolymers, such as consistometer consistency and viscosity were examined besides their mechanical properties. The investigation of mechanical properties included uniaxial compressive strength, sonic strength and tensile strength. The pumpability and setting time have been studied by changing mix design of the geopolymeric slurries along with the addition of selected retarders. Finally, microstructure of the cured geopolymers was studied using Scanning Electron Microscopy (SEM). The results show that slurries have a non-Newtonian behavior like a Bingham material with a small yield stress. The curing pressure reduced the pumpability of the geopolymeric slurries; however, the reason remained unclear. Addition of sucrose by 1.2 wt.% of the total solid content resulted in an optimal accumulative heat release, which showed the highest strength development. Pumpability of the mixes was prolonged by introducing sucrose to the geopolymeric slurries. Tensile strength of the geopolymers was found to be approximately 5 percent of their compressive strengths.

Well integrity has an utmost importance for upstream operations that has resulted in many studies to improve zonal isolation. Few papers comprehensively investigated the elements involved in cementing service delivery that are conducive to both well integrity and zonal isolation for extreme high temperature conditions. Geothermal, High Temperature and High Pressure, Steam Assisted Gravity Drainage (SAGD), Cyclic Steam Stimulation (CSS) (also known as Steam Flood) and Fire Flooding are all examples where the cement sheath can experience extreme high temperatures. This study emphasizes on sustainable zonal isolation throughout the life of wells facing extreme high temperatures. The purpose of this paper is to present the challenges of extreme high temperature cementing and show solutions used to assure cement integrity under such extreme environments. These challenges were reviewed and the most up to date solutions were discussed. The examples explained through this paper demonstrate the role of these critical elements for safe and environmentally friendly extreme high temperature well cementing. This analysis provides recommendations to sustain long-term zonal isolation when operations involve with extreme high temperature conditions.

The foremost function of primary cementing is to achieve zonal isolation and ensure long-term cement integrity during the lifetime of the well. Current advanced drilling and cementing technologies enable the production of oil and gas in more complex and challenging conditions such as deep wells and unconventional wells either onshore or offshore. Understanding the mechanical performance of cement sheath under downhole conditions, therefore, is crucial for successful cementing operations. Unfortunately, most published mechanical data were still limited to the compressive and tensile strengths determined at ambient condition as well as Young's modulus. The result for tensile strength varies greatly due to the lack of API standard tensile strength testing. The purpose of this study is to evaluate the additive-additive interaction on cement mechanical properties. Individual additives and their combinations were mixed with class H cement at a density of 16 ppg and cured under elevated temperature and pressure. The mechanical properties tested at ambient and curing conditions include compressive, tensile and yield strength, Young's modulus, and Poisson's ratio. The cement mechanical performances measured at curing conditions, especially the tensile strength, were different from the results obtained at ambient conditions. The elasticity of cement was improved by fiber and polymeric additives tested in this work. This study provides comprehensive experimental data on how the slurry formulation, chemical characteristics of the additives, and additive-additive interactions can affect cement mechanical properties. This study also gives insights into the correlations among various mechanical properties, and the key parameters that could determine cement elasticity. The results can be used as direct guidance for future field applications.

Achieving zonal isolation has always been a challenge when drilling and cementing gas-producing wells in a high-pressure/high-temperature (HP/HT) environment. A generally accepted definition of a HP/HT well is one in which the undisturbed bottomhole temperature at prospective reservoir depth or total depth is greater than 149°C [300°F] and either the maximum anticipated pore pressure of any porous formation to be drilled exceeds a hydrostatic pressure gradient of 97 Pa/m [0.8 psi/ft] or pressure control equipment with a rated working pressure in excess of 68.94 Mpa [10,000 psi] is required. In the past, HP/HT wells were drilled and cemented in the UAE using conventional cementing design and techniques. Those wells had zonal isolation concerns for cemented production strings, proving that cementing was a critical factor in the HP/HT field. In addition, the wells must bear the stresses generated from injection pressure and temperature changes and frequent cycling of injection during well testing and production. Trapped gas and oil between production and intermediate casing (abnormal annular wellhead pressure) has been globally recognized as one of the serious challenges faced by the Industry from well security and isolation perspective. To tackle the potential safety and environmental hazards of abnormal annulus pressure, better cementing practices and solutions are introduced to improve well life cycle and minimize the frequency of workover operations. This case describes the use of self-healing cement and flexible and expandable cement to prevent cement failure due to induced stresses and optimize the isolation and ultimately deliver on the objective set for critical exploration well by the Operator.