Summary Successful reservoir surveillance and production monitoring is a key component for effectively managing any field production strategy. For production logging in openhole horizontal extended reach wells (ERWs), the challenges are formidable and extensive; logging these extreme lengths in a cased hole would be difficult enough but is considerably exaggerated in the openhole condition. A coiled-tubing (CT) logging run in open hole must also contend with increased frictional forces, high dogleg severity, a quicker onset of helical buckling, and early lockup. The challenge of effectively logging these ERWs is further complicated by constraints in the completion where electrical submersible pumps (ESPs) are installed, including a 2.4-in. bypass section. Although hydraulically powered CT tractors already existed, a slim CT tractor with real-time logging capabilities was not available in the market. In partnership with a specialist CT tractor manufacturer, a slim logging CT tractor was designed and built to meet the exceptional demands of pulling the CT to target depth (TD). The tractor is 100% hydraulically powered, with no electrical power, allowing for uninterrupted logging during tractoring. The tractor is powered by the differential pressure from the bore of the CT to the wellbore and is operated by a preset pump rate from surface. Developed to improve the low coverage in openhole ERW logging jobs, the tractor underwent extensive factory testing before being deployed to the field. The tractor was rigged up on location with the production logging tool and run in hole (RIH). Once the CT locked up, the tractor was activated and pulled the coil to cover more than 90% of the openhole section, delivering a pulling force of up to 3,200 lbf. Real-time production logging was conducted simultaneously with the tractor activation; flowing and shut-in passes were completed to successfully capture the zonal inflow profile. Real-time logging with the tractor is logistically efficient and allows instantaneous decision making to repeat passes for improved data quality. The new slim logging tractor (SLT) is the world’s slimmest and most compact and is the first CT tractor of its kind to enable production logging operations in openhole horizontal ERWs. The importance of the ability to successfully log these ERWs cannot be overstated; reservoir simulations and management decisions are only as good as the quality of data available. Some of the advantages of drilling ERWs, such as increased reservoir contact, reduced footprint, and fewer wells drilled, will be lost if sufficient reservoir surveillance cannot be achieved. To maximize the benefits of ERWs, creative solutions and innovative designs must be developed continually to push the boundaries further.

Summary Intermittent flow is one of the most complex flow regimes in horizontal pipes. Various studies have classified this regime as two distinct subregimes: plug and slug flow. This classification has been made based on flow observations. In this work, the behavior of several flow parameters that characterize plug and slug flow are presented. Data from eight published works in the open literature were collected and studied to explain the behavior of both regimes. These data include pressure drop, void fraction, and slug frequency, as well as the lengths of liquid slugs and elongated bubbles for slug and plug regimes. It is observed from the evolution and analysis of these parameters that plug and slug flows have several different distinct features and should be considered as two separate regimes for the empirical modelization of the hydrodynamic parameters. The mixture Froude number, and to a lesser extent the liquid superficial velocity to gas superficial velocity ratio, seem to have significant impacts on the plug-to-slug flow transition.

Summary Most of the existing slug (SL) to churn (CH) or SL to pseudo-slug (PS) transition models (empirical and mechanistic) account for the effect of the SL liquid holdup ( H LS ). For simplicity, some of these models assume a constant value of H LS in SL/CH and SL/PS flow transitions, leading to a straightforward solution. Other models correlate H LS with different flow variables, resulting in an iterative solution for predicting these transitions. Using an experimental database collected from the open literature, two empirical correlations for prediction H LS at the SL/PS and SL/CH transitions ( H LST ) are proposed in this study. This database is composed of 1,029 data points collected in vertical, inclined, and horizontal configurations. The first correlation is developed for medium to high liquid viscosity two-phase flow ( μ L > 0.01 Pa·s), whereas the second one is developed for low liquid viscosity flow ( μ L ≤ 0.01 Pa·s). Both correlations are shown to be a function of superficial liquid velocity ( V SL ), liquid viscosity ( μ L ), and pipe inclination angle ( θ ). The proposed correlations in a combination with the H LS model of Abdul-Majeed and Al-Mashat (2019) have been used to predict SL/PS and SL/CH transitions, and very satisfactory results were obtained. Furthermore, the SL/CH model of Brauner and Barnea (1986) is modified by using the proposed H LST correlations, instead of using a constant value. The modification results in a significant improvement in the prediction of SL/CH and SL/PS transitions and fixes the incorrect decrease of superficial gas velocity ( V SG ) with increasing V SL . The modified model follows the expected increase of V SG for high V SL , shown by the published observations. The proposed combinations are compared with the existing transition models and show superior performance among all models when tested against 357 measured data from independent studies.

Summary The objective of this study is the experimental and theoretical investigation of the fall mechanics of continuous flow plungers. Fall velocity of the two-piece plungers with different sleeve and ball combinations and bypass plungers are examined in both static and dynamic conditions to develop a drag coefficient relationship. The dimensionless analysis conducted included the wall effect, inclination, and the liquid holdup correction of the fall stage. A fall model is developed to estimate fall velocities of the ball, sleeve, and bypass plungers. Sensitivity analysis is performed to reveal influential parameters to the fall velocity of continuous flow plungers. In a static facility, four sleeves with different height, weight, and outer diameter (OD); three balls made with different materials; and a bypass plunger are tested in four different mediums. The wall effect on the settling velocity is defined, and it is used to validate the ball drag coefficient results obtained from the experimental setup. Two-phase flow experiments were conducted by injecting gas into the static liquid column, and the liquid holdup effect on the drag coefficient is observed. Experiments in a dynamic facility are used for liquid holdup and deviation corrections. The fall model is developed to estimate fall velocities of the continuous flow plungers against the flow. Dimensionless parameters obtained in the experiments are combined with multiphase flow simulation to estimate the fall velocity of plungers in the field scale. Reference drag coefficient values of plungers are obtained for respective Reynolds number values. Experimental wall effect, liquid holdup, and inclination corrections are provided. The fall model results for separation time, fall velocity, total fall duration, and maximum flow rate to fall against are estimated for different cases. Sensitivity analysis showed that the drag coefficient, the weight of plungers, pressure, and gas flow rate are the most influential parameters for the fall velocity of the plungers. Furthermore, the fall model revealed that plungers fall slowest at the wellhead conditions for the range of gas flow rates experienced in field conditions. Lower pressure at the wellhead had two opposing effects; namely, reduced gas density, thereby reducing the drag and gas expansion that increased the gas velocity, which in turn increased the drag. Estimating fall velocity of continuous flow plungers is crucial to optimize ball and sleeve separation time, plunger selection, and the gas injection rate for plunger-assisted gas lift (PAGL). The fall model provides maximum flow rate to fall against, which is defined as the upper operational boundary for continuous flow plungers. This study presents a new methodology to predict fall velocity using the drag coefficient vs. Reynolds number relationship, wall effect, liquid holdup, deviation corrections, and incorporating multiphase flow simulation.

Summary One of the enduring pieces of the jigsaw puzzle for all unconventional plays is drawdown (DD), a technique for attaining optimal return on investment. Assessment of the DD from producing wells in unconventional resources poses unique challenges to operators; among them the fact that many operators are reluctant to reveal the production, pressure, and completion data required. In addition to multiple factors, various completion and spacing parameters add to the complexity of the problem. This work aims to determine the optimum DD strategy. Several DD trials were implemented within the Anadarko Basin in combination with various completion strategies. Privately obtained production and completion data were analyzed and combined with well log analysis in conjunction with data analytics tools. A case study is presented that explores a new strategy for DD producing wells within the Anadarko Basin to optimize a return on investment. We use scatter-plot smoothing to develop a predictive relationship between DD and two dependent variables—estimated ultimate recovery (EUR) and initial production (IP) for 180 days of oil—and introduce a model that evaluates horizontal well production variables based on DD. Key data were estimated using reservoir and production variables. The data analytics suggested the optimal DD value of 53 psi/D for different reservoirs within the Anadarko Basin. This result may give professionals additional insight into more fully understanding the Anadarko Basin. Through these optimal ranges, we hope to gain a more complete understanding of the best way to DD wells when they are drilled simultaneously. Our discoveries and workflow within the Woodford and Mayes Formations may be applied to various plays and formations across the unconventional play spectrum. Optimal DD techniques in unconventional reservoirs could add billions of dollars in revenue to a company’s portfolio and dramatically increase the rate of return, as well as offer a new understanding of the respective producing reservoirs.

Summary Accurate zonal flow rate determination is necessary for better reservoir behavior understanding and for making important decisions that can improve well productivity. Knowledge of the capabilities of different reservoir zones in the same well also has significant importance in reservoir performance monitoring and selection of perforation intervals in development wells. Conventional production log analysis techniques can usually yield good results only if the fullbore spinner readings are reliable. However, the fullbore spinner measurement may not be available in some wells. Examples include cases in which the fullbore spinner cannot access the well due to mechanical obstruction, or when the casing is not clean enough, causing potential plugging of fullbore spinner blades. In these situations, the fullbore flow-rate readings may not be available or at least unclear or confusing, which may lead to incorrect decisions. In many of these situations, inline spinner (ILS) data may be readily available. The ILS is often used for qualitative interpretation (i.e., determining which zones are producing), but there is not a specific method to use the ILS for a quantitative solution in the absence of surface measurements of rates. In this paper, we introduce a new method to calculate the volumetric zonal flow rate using ILS data with high accuracy. Approximately 40 oil wells are used to develop an empirical correlation to compute zonal flow rates from ILS data in casing strings. The new method was used to quantitatively interpret eight oil wells for validation. In these wells, fullbore and ILS data were significantly different. The new method for interpretation of ILS data provided results consistent with surface production tests and led to decisions that contributed to increasing production rates.

Summary Gerotors are positive displacement pumps and potential artificial lift options in the oil and gas industry. This study presents the performance characteristics from physical testing of a unique one-stage, equal-walled gerotor pump design operating in oil and oil/air mixtures. The pump was tested at various rotational speeds in a flow loop. The performance results were obtained to ascertain potential design optimizations of the pump before embarking on manufacturing and testing of the field prototype pump. A physical prototype of a one-stage 400 series gerotor pump, suitable for application in a 5.5-in. casing, was designed, manufactured, assembled, and tested. Mineral oil and air were used as the operating media. For given pump outlet valve settings, the pump rotational speeds were set to 200, 250, 300, and 350 rev/min. Gas volume fractions (GVFs) at the pump inlet were varied from 0% to the maximum the current pump design could handle. For each test point, the corresponding pump parameters were measured. Dimensionless performance plots were established for obtaining pump performance at other flow conditions. The results showed that pump flow rate decreased with increasing differential pressure, typical of positive displacement pumps. At 200 and 350 rev/min, maximum pump delivery is approximately 190 and 330 B/D of oil, respectively, at zero differential pressure. The pump can supply flow against a differential pressure of up to approximately 5.5 psi at 200 rev/min and 15 psi at 350 rev/min. For the 200 to 350 rev/min speed range, volumetric efficiencies varied from 30 to 73%, whereas the electric power input varied from 145 to 191 W. When pumping oil/air mixtures, the current gerotor pump design can handle 15% GVF maximum, at 250, 300, and 350 rev/min. For certain pump outlet pressures, the total fluid flow rates decreased as the GVF increased to 15%. The volumetric efficiencies at 15% GVF varied from 32 to 53% for the 300 to 350 rev/min speed range, whereas the motor electric power input decreased with increasing GVF up to 15%. In conclusion, increasing the pump rotational speed improves the volumetric efficiency and gas-handling capability of the gerotor pump. These observations will aid in the required design optimization to enhance the performance of the future field prototype gerotor pump. This study presents the capabilities of gerotors as potential artificial lift alternatives to handle liquid and gas/liquid mixtures for boosting applications in oilfield operations. The technology with additional design optimization can be readily integrated into oilfield equipment architecture. The mechanical simplicity of gerotors and their compactness provides a promising artificial lift substitute that may be implemented for downhole or surface production of liquid or gas/liquid mixtures in the oil and gas industry.

Summary We propose a novel method for estimating average fracture compressibility c f ¯ during flowback process and apply it to flowback data from 10 multifractured horizontal wells completed in Woodford (WF) and Meramec (MM) formations. We conduct complementary diagnostic flow-regime analyses and calculate c f ¯ by combining a flowing-material-balance (FMB) equation with pressure-normalized-rate (PNR)-decline analysis. Flowback data of these wells show up to 2 weeks of single-phase water production followed by hydrocarbon breakthrough. Plots of water-rate-normalized pressure and its derivative show pronounced unit slopes, suggesting boundary-dominated flow (BDF) of water in fractures during single-phase flow. Water PNR decline curves follow a harmonic trend during single-phase- and multiphase-flow periods. Ultimate water production from the forecasted harmonic trend gives an estimate of initial fracture volume. The c f ¯ estimates for these wells are verified by comparing them with the ones from the Aguilera (1999) type curves for natural fractures and experimental data. The results show that our c f ¯ estimates (4 to 22×10 −5 psi −1 ) are close to the lower limit of the values estimated by previous studies, which can be explained by the presence of proppants in hydraulic fractures.

Summary In multiple-stage hydraulic fracturing treatments performed in horizontal wells, treatment confinement is the state in which fracturing fluid and proppant flow out of the wellbore only through the specific perforations targeted for the fracturing stage. The terms treatment confinement and treatment isolation are synonymous. Isolation from previously treated intervals is a necessary condition for efficient treatment along the lateral. Failure to confine fracturing stages can be a result of failure of the fracture plug to maintain a seal or the development of casing breaches (holes) in the proximity of the fracture plug. Both conditions can be strongly impacted by proppant induced erosion. This paper is a sequel to a previous publication in which casing erosion and breaches were investigated in fracture treated horizontal wells in the Montney Formation ( White et al. 2020 ). Integrated diagnostic methods based on data from treating pressure analysis, fiber-optic measurements, and downhole imaging were applied to investigate the root cause of failure. It was determined that treatment pressure analysis was effective in diagnosing casing and associated fracture plug integrity-loss events. This was achieved by (1) identifying treating pressure trends and anomalies during the main part of the treatment that signify confinement loss, (2) calculating near-wellbore friction at the end of treatments to compare to the friction expected for a confined treatment, and (3) analyzing step-down tests conducted during the pad stage and overflush stage at the end of the treatment to determine the near-wellbore frictional components of perforation friction and near-wellbore tortuosity. This information enables comparison of previous with current treatments for determining the effects of job design and fracture plug modifications on treatment confinement. The objective of this paper is to validate that useful conclusions on the degree of treatment confinement can be made using only stand-alone pressure-based analysis. This is achieved by comparing the analysis results with fiber-optic and post-treatment wellbore imaging measurements. Also highlighted is the use of downhole gauges for accurately calculating pipe friction, which is necessary for accurately calculating bottomhole treating pressure at the active treatment interval.

Summary In this study, we investigate the effect of liquid viscosity ( μ L ) on the slug/churn transition in gas/liquid flows in vertical pipes. A total of 80 experimental churn-flow data points from two different sources are compiled as a data set, covering liquid viscosities from 17.23 to 586 mPa·s. Air was used in these studies as a gas phase with two different liquids, aqueous glycerol and a commercial synthetic mineral oil, flowing in vertical pipes of 0.0192- and 0.0508-m inner diameter (ID). The data set is used to examine the existing slug/churn-flow-transition models and provide further insights into the effect of μ L on the transition. The existing models are categorized into two groups according to their response of the slug/churn transition to the increase in liquid superficial velocity ( V sl ) on the V sg / V sl flow map. The first category exhibits a decrease in superficial gas velocity ( V sg ) with the increase in V sl at slug/churn (the transition concave to the left). The other one predicts an increase in V sg with increasing of V sl (the transition concave to the right). Analysis of the data set reveals that on the V sg / V sl flow map, the slug/churn transition moves toward lower superficial gas velocities as liquid viscosity increases and occurs approximately at a constant V sg for low to medium V sl . The predictions of these models were tested against the data set and poor results were shown by most models. The best performance is given by the Abdul-Majeed (1997) model. A dimensional analysis is applied in the present study to develop a new slug/churn-transition model. This analysis indicates that the transition is related to three dimensionless numbers, namely gas- and liquid-phase Froude numbers, in addition to the inverse liquid-viscosity number. An improved revision to the Abdul-Majeed model is achieved using these three dimensionless numbers. The revision enables the model to predict the transition for low, medium, and high liquid viscosity. The revised model clearly outperforms all the existing models for the present data and viscous data from independent studies. Furthermore, the revised model exhibits the expected trend against changes in pipe diameter and gas density.

Liquid-liquid phase flow in pipes merits further investigation as a challenging issue that has very rich physics and is faced in everyday applications. It is the main problem challenging the fluid flow mechanism in the oil and gas industry. The pressure gradient of liquid flow and flow pattern are still the topics of numerous research projects. In this paper, the emphasis is on further investigation to research the flow pattern, water holdup (HW), and pressure decrease for vertical, horizontal, and inclined flow directions of oil and water flows. Test section lines of 4.19-in. (106.426 mm) inner diameter (ID) and 5-m horizontal, 5-m inclined, and 5-m vertical test sections were serially connected. The experiments were conducted at 40°C using 2-cp viscosity oil and tap water, and oil density of 850 kg/m 3 , at the standard conditions. Fifty experiments were executed at 250 kPa at the multiphase flow test facility, with horizontal, upward (0.6° and 4°), downward (−0.6° and −4°) hilly terrain and vertical pipes. The oil and water superficial velocities were changed between 0.03 and 2 m/s. This evidence was obtained using video recordings; the flow patterns were observed, and the selection of each flow pattern was depicted for each condition. For horizontal and inclined flow, new flow patterns were documented (e.g., oil transfer in a line forms at the top of the pipeline, typically at high water rate, and water transfer at the lower part of the pipe at a high oil rate). The data were taken at each flow condition, resulting in new holdup and pressure drop. The results show that the flow rate and the pipe inclination angle have major impacts on the holdup and pressure drop performances. In the vertical flow, a clear peak was demonstrated by experiments after the superficial oil velocity reached a certain value. This peak is known as phase inversion point, where after this peak, the pressure starts declining as the superficial oil velocity increases. Also, slippage has been observed after varying inlet oil flow rates between the two phases. The experiments showed that with minor alteration in the inclination angle, the slippage was significantly changed. This study presented new experimental results (measured mainly at horizontal, inclined, and vertical flow conditions) of HW, flow pattern, and pressure drop. These findings are key evidence of the evolving oil-water and flowline estimate models.

Summary In the first part of this work, the development of a capital cost optimization model for sizing three-phase separators was described. The developed model uses generalized reduced gradient nonlinear algorithms to determine the minimum cost associated with the construction of horizontal separators subject to four sets of constraints. In the second part, an experimental test rig was designed and used to investigate the effect of gas flow rate, liquid flow rate, and slenderness ratio ( L / D ) on the separation performance of horizontal three-phase separators. The results indicated an inverse relationship between an increase in gas and liquid flow rate and the separator outlet quality. It also indicated a direct relationship between an increase in slenderness ratio and separator outlet quality. The results also showed that the gradient change of the percentage of water in the oil outlet with respect to slenderness ratio decreased to ratios of 6:1. Hence, the separation rate increased. At ratios greater than 6:1, the separation still increases, but the gradient change in separation drops off, implying that the benefit in terms of separation is diminishing beyond this point. Therefore, the optimal slenderness ratio for technical reasons is 6:1.

Summary One of the most critical issues in the oil and gas industry is the dewatering of the pipelines used for natural gas transportation, and foam injection seems to be a prominent solution. This work has two goals: The main one concerns the development of an optical tool to measure the liquid holdup in foamy flows and perform the flow regime characterization, whereas the secondary goal is to quantify the effectiveness of surfactant injection in reducing the liquid loading. In this paper, we present the results of an experimental campaign aimed at the characterization of gas-liquid-foam flows in a horizontal pipe. Initially, liquid loading measurements for gas and liquid superficial velocities, ranging from 0.41 to 2.30 m/s and from 0.03 to 0.06 m/s, respectively, were performed by means of a specifically developed optical method. For each liquid superficial velocity, the minimum liquid holdup was found to lie in the proximity of the boundary between plug and stratified flow regime, with a superficial gas velocity between 0.44 and 0.90 m/s. Hence, the plug flow region corresponds to the best operating condition to perform the pipeline dewatering procedure. Moreover, the drift-flux model usually adopted for ordinary two-phasegas-liquid flows seems to fit well with the measured values of void fraction.

Summary Multiphase flowmetering is a requirement across a range of process industries, particularly those that pertain to oil and gas. Generally, both the composition and individual phase velocities are required; this results in a complex measurement task made more acute by the prevalence of turbulent flow and a variety of flow regimes. In the current review, the main technical options to meet this metrology are outlined and used to provide context for the main focus on the use of nuclear magnetic resonance (NMR) technology for multiphase flowmetering. Relevant fundamentals of NMR are detailed as is their exploitation to quantify flow composition and individual phase velocities for multiphase flow. The review then proceeds to detail three NMR multiphase flowmeter (MPFM) apparatus and concludes with a consideration of future challenges and prospects for the technology.

Summary The litmus test for downhole multiphase flowmeters is to compare the measured phase flow rates with the rates from a test separator or other surface measurement systems. In most cases, the composition of the measurand is required for flowmeters. This is typically obtained from bottomhole fluid samples. Extracting and analyzing fluid samples is an expensive process mostly done at the initial stages of field development. In some cases, the composition may be old or unavailable, leading to subpar flowmeter performance compared to surface systems. In this work, it is shown that when the data from a surface system such as a test separator are used in conjunction with the mixture sound speed measured downhole, it is possible to optimize a downhole multiphase flowmeter system without obtaining new fluid samples. The optimization process is independent of the downhole measurement device because the required flow-velocity and sound-speed measurements may be obtained from separate devices. For example, the fluid bulk velocity and mixture sound speed can be measured by a local measurement device and a distributed acoustic sensing (DAS) system, respectively. The main challenge in a flow-velocity/sound-speed measurement system is determining individual phase sound speeds so that the mixture phase fraction can be correctly determined using Wood’s mixture sound speed model. The phase fraction from the separator tests can be used as the target value to optimize the performance of the system. The system has two operation modes. In optimization mode, the individual phase sound speeds are calculated backward using the predicted phase fractions from surface measurements. Pressure and temperature variations at measurement locations, as well as pipe compliance effects, are accounted for during the process. After the adjustment of individual phase sound speeds, steady-state operation mode takes over, and a forward calculation is implemented using the same model. The final phase fraction agrees well with the actual value and can be improved further with an iterative approach. This novel method is demonstrated in a North Sea case history. A downhole optical flowmeter in a North Sea field measured mixture velocity and sound speed. Well-test results indicated that water cut from the flowmeter was underreported and phase flow rates did not match test-separator rates. Instead of halting production and going through a fluid sample analysis cycle, the test-separator water cut was used as the target value to optimize oil phase sound speed using Wood’s model in the optimization mode. The difference between the initial and optimized oil sound speeds was extrapolated to other pressure and temperature conditions, and steady-state operation mode showed that separator tests and flowmeter measurements closely matched. Subsequent flowmeter and test-separator data confirmed excellent agreement. Using surface measurements and downhole mixture sound speed to optimize phase flow rates is a novel method that has not been previously demonstrated. This method is independent of device type, is broadly applicable, and improves the understanding of multiphase flow measurement.

Summary What do you do after plunger lifting? What if lift gas is not readily available or your liquid level is around a bend? What can you do with a well that has low reservoir pressure, liquid-loading trouble, and fragile economics? Do you give up on the remaining reserves and advance to plugging and abandonment? These questions were considered, and the answers were found to be unsatisfactory. This paper will describe the development and testing of a novel wireline-deployed positive-displacement pump (WLPDP) that was invented to address these challenges. Artificial-lift (AL) pumps have historically been developed with high-producing oil wells in mind. Pumps for late-life wells have mostly been repurposed from these applications and optimized for reduced liquids production. The WLPDP development began with the constraints of late-life wells with the goal of addressing reserves that conventional AL methods would struggle to produce profitably. Internal and industry-wide data were first reviewed to determine what WLPDP specifications would address the majority of late-life wells. The primary target was gas wells, although “stripper” oil wells were also considered. The resulting goal was a pump that could deliver 30 BFPD from 10,000-ft true vertical depth (TVD). The pumping system must be cost-effective to be a viable solution, which led to several design boundaries. Pumps fail and replacement costs can drive economics, so the system must be deployable/retrievable through tubing. The majority of new onshore wells have tortuous geometries, so the system must be able to function at the desired depth despite them—without damaging associated downhole components. The system should use as many off-the-shelf components and known technologies as possible to reduce development costs and encourage integration. Finally, the pump should be able to handle a variety of wellbore liquids, produced gases, and limited solids. The WLPDP was designed to meet the established specifications and boundary conditions. The 2.25-in.-outer-diameter (OD) pump is deployed through tubing. and powered with a standard wireline (WL) logging cable. The cable powers a direct-current (DC) motor that drives an axial piston pump. The piston pump circulates a dielectric oil between two bladders by means of a switching valve. When each bladder expands, it pressurizes inlet-wellbore liquids, pushing them out of the well. Produced gas flows in the annulus between the tubing and production casing. The intake/discharge check valves and bladders are the only internal pump components that contact the wellbore fluids. The WLPDP system was able to meet the design-volume/pressure specifications in all orientations, as confirmed through laboratory and integration testing. Targeted studies were conducted to verify/improve check-valve reliability, gas handling, elastomer suitability, and cable-corrosion resistance. The results of these and related studies will be discussed in the paper.

Summary In this paper, we introduce pumpdown diagnostics, an economical process in which cement sheath integrity, perforation cluster spacing, and fracturing (frac) plug integrity can be assessed for every fracturing stage, potentially leading to improvements in stimulation, completion, cementing, and drilling practices. It is based on analyzing wellbore pressure responses occurring at key segments of the wireline pumpdown and perforating operation and correlating the results among multiple fracturing stages and wells in a field or play. A special requirement is that the ball check is inserted in the frac plug and pumped to seat prior to performing perforating operations. A complementary benefit of this process is that selectively establishing injectivity in the most distant perforation cluster can be used to establish inhibited hydrochloric (HCl) acid coverage across all perforation intervals for uniform reduction in near-wellbore tortuosity. Reviews of pumpdown diagnostics field cases from several unconventional plays provide the following insights. Pumpdown diagnostics are time efficient and economical, requiring approximately 15 minutes per fracturing stage. Evaluating communication to the previous fracturing stage can serve as a key performance indicator for treatment control or cement sheath integrity. Pumpdown diagnostic results can be more reliable than cement bond log evaluation, and stage isolation characteristics can be strongly affected by cluster spacing.

Summary Distributed temperature sensing (DTS) is a valuable tool to diagnose multistage hydraulic fracture treatments. When a stage interval is shut in, the clusters that take more fluid during pumping warm up more slowly. Therefore, the fluid volume injected into each cluster can be quantitatively interpreted by numerical inversion of the warm-back temperature behavior. This general concept assumes that the different warm-back behavior is controlled by only the injected fluid volume; however, recent observations of DTS data indicate that completion configurations significantly influence the warm-back behavior. This paper investigates the completion effects on the DTS interpretation. In ideal conditions, when a stage is fractured, the upstream stage intervals should show an almost uniform temperature that is close to the injected fluid temperature. This is due to the high fluid velocity of injected fluid in the wellbore, and the upstream intervals have not been perforated (noncommunicating intervals), so the only heat transfer is heat conduction between the wellbore fluid and the surrounding reservoir. But the field DTS data show considerably irregular variations in temperature along the upstream stage intervals. These variations are caused by the completion effects. The nonuniform temperature profile is caused by different heat transfer behavior induced by completion hardware along the production casing string, such as joints, clamps, and blast protectors, and by the sensing cable location in the cement, as well as the cement quality. Because the varying heat transfer behavior impacts the warm-back behavior as well as the temperature profile, the completion effects need to be considered in DTS interpretation. A method of DTS interpretation considering the completion effects to diagnose multistage fracture treatments was developed. Because the heat transfer between a wellbore and a reservoir depends on the overall heat transfer coefficient describing heat conduction through the completion in a forward model, this parameter needs to be tuned all along the wellbore. To calibrate the completion effect, the temperature inversion is conducted using the temperature measured at a stage interval that is upstream of a stage interval currently being treated. Because the interpreted stage interval is not perforated at that time, the thermal behavior at the noncommunicating interval is governed by only the heat conduction through the completion environment. Once the effective values of the overall heat transfer coefficient are estimated along the interpreted stage interval, they can be assumed to be constant physical parameters. Then, the fluid volume distribution is interpreted by using the effective overall heat transfer coefficient profile along each interval. This study provides a field application of the developed interpretation method. The new interpretation method provides more accurate diagnosis of fracture treatments by DTS interpretation.

With the use of chemically based enhanced-recovery methods, water management, which has always been a major point in the production-operation processes, needs to be considered and adapted because the whole water cycle will be affected by the backproduced additives. Enhanced-oil-recovery (EOR) chemicals such as alkali molecules, high-molecular-weight polymers, or surfactant formulation will dramatically modify pH, viscosity, and phase behaviors of produced fluids. The main issues encountered in oil/water-separation processes are directly related to the risk of tight emulsion formation, which might considerably complicate the surface-water-treatment processes. The objective of this paper is to underline the effect of one of these chemicals, a surfactant formulation, on the produced-water cycle when they are backproduced first at a laboratory scale and second on a large-scale separation unit using an industrial-size flow loop and a well-instrumented separator. Our goal is first to investigate the impact of surfactant on the water/oil mixture separation efficiency, and second, to find an efficient demulsifier specific for this case. At the laboratory scale, the impact of surfactant within produced fluids on oil/water separation (regarding separation kinetics but also oil/water phase qualities) will be evaluated by performing bottle tests. Those laboratory bottle tests enabled us to screen different parameters, such as the surfactant concentration, the water cut that can strongly affect the type of formed emulsion [oil in water (O/W) or water in oil (W/O)], and its stability. The oil/water phase qualities were quantified and correlations with parameters related to the large-scale experiment were drawn, helping us in defining the key parameters for this campaign. Indeed, to get closer to a field case, a semi-industrial-scale test platform was used. The flow loop reproduces separation process conditions encountered in a field treatment facility, including the production separator, the controlled temperature, and the oilfield chemical injection rate. The main operating conditions are liquid flow rates and temperature. The influence of different parameters can be studied, such as the surfactant concentration, mixing conditions, residence time, water cut, and the presence of chemicals that will help the separation process. Different types of emulsions were formed depending on the conditions, and their stability was evaluated through the measurement of separation profiles using a single electrode capacitance probe (SECAP) within the separator. The results obtained show how the surfactant, as well as the demulsifier concentration, have led to different types of emulsions and have affected the oil/water separation processes. These tests have confirmed that separation is more difficult in the presence of surfactant and that water quality was degraded. It has also been shown that separation processes can be greatly improved by adding some EOR-compliant demulsifier to recover a better water quality compared with the surfactant case. Laboratory workflows, as well as experiments performed at large scale using an industrial size separator, could help to minimize risks of operations to mitigate these challenges in terms of separation issues. This work illustrates that water management is a major challenge for produced fluids containing EOR chemicals that need an integrated approach and should be studied beforehand.

Summary Productivity of multistage‐fractured gas wells is possibly degraded by conductivity impairments and non‐Darcy flow during long‐term production. Such degradations are pronounced by flow convergence to short perforated intervals, while it is challenging to identify degraded stages for remediation. Moreover, remedial actions can be expensive under a high‐pressure/high‐temperature (HP/HT) environment. A field case demonstrates successful application of reperforation as a cost‐effective way to mitigate the flow convergence by prioritizing targets with multirate production‐logging (PL) results. This work presents theoretical investigations using numerical simulations and field execution of reperforation for a well with six‐stage fracturing treatments in a HP/HT volcanic gas reservoir onshore Japan. Apparent conductivity reduction was suspected during more than 15 years of production, and it was pronounced by non‐Darcy flow effects associated with flow convergence to short perforated intervals. Multirate PL was used to identify impaired stages by quantifying the inflow‐performance relationship (IPR) of each stage under transient flow‐after‐flow (FAF) testing. The impaired stages were reperforated, adding perforation intervals with wireline‐conveyed perforators. Pressure‐buildup (PBU) tests before and after the job and post‐job PL were used to validate productivity improvements. Target zones for reperforations were identified and prioritized with results of the multirate PL conducted. The stage IPRs were drawn, and relatively large non‐Darcy effects were identified in three stages by shapes of the IPRs and/or decreasing inflow contributions as the surface rate increased. Also, a temperature log showed steep temperature change at the bottom of the fourth stage; the fracture might propagate below the perforated interval. Ranges of production increment were estimated using a numerical model calibrated against the estimated stage IPRs. The estimated increment was in the range of 15 to 30% with the planned reperforation program, while its magnitude depended on the connection between new perforations and existing fractures. Afterward, the reperforation job was performed and the gas rate was confirmed to be increased by 26% with the same wellhead pressure after 1 month of production. The post‐job PL was conducted 3 months after the reperforation. The well IPR was improved, implying reduction of the non‐Darcy effects. Results of PBU tests also indicated reduction of skin factor. The stage IPRs were redrawn with the post‐job PL, and they suggested clear improvements in two stages where screenout occurred during fracturing treatments and a stage where significant non‐Darcy effect was suspected. The workflow and strategy in this paper can be applied for productivity restoration in a cost‐effective way to multistage‐fractured gas wells with short perforated intervals and impaired apparent conductivity during long‐term production. Especially, the interpreted results suggested effectiveness of the proposed approach for productivity improvement in stages where screenout occurs during fracturing treatments. Moreover, lessons learned on the importance of careful test designs for PL were discussed because they are keys for success.