Reservoir Section Research Articles

Experimental Study on Yield Strength Variation Law of Casing Materials under Alternating Thermal–Mechanical Coupling Loads

Unconventional oil and gas reservoirs, characterized by low porosity and permeability, often require multistage fracturing techniques for development. The high-pressure fracturing fluids with large volumes can easily cause alternating changes in both temperature and pressure within the casing. Using a theoretical model and field data from hydraulic fracturing operations, this paper calculated the alternating ranges of axial loads and temperatures in the reservoir section. Based on the calculation results, the temperature–load alternating coupling test of the P110 casing was carried out, and the tensile test was performed to analyze the yield strength variation law of the casing material. The results indicate that the yield strength, ultimate strength, and elastic modulus of casing materials are decreased under alternating thermal–mechanical coupling conditions. As the number of alternating cycles increases, there is an initial rapid decrease followed by a slower declining trend. Moreover, the tension–tension (T–T) cycles induce greater reductions in yield strength and ultimate strength than tension–compression (T–C) cycles. Meanwhile, under the same axial load condition, the higher the circulating temperature, the more significant the reduction in yield strength and ultimate strength. In essence, this is the result of the coupling effect of low-cycle fatigue and temperature aging. Finally, based on the experimental data, a yield strength prediction model of the P110 casing under the alternating thermal–mechanical coupling condition was established. The research results provide theoretical guidance for the safe design and material selection of a casing string under multistage volumetric fracturing conditions of shale gas exploration.

Preliminary Insight into Ice Melting, Surface Subsidence, and Wellhead Instability during Oil and Gas Extraction in Permafrost Region

Oil and gas production in permafrost can effectively alleviate energy tensions. However, ice melting around wellbores and the accompanying wellhead instability affect the efficiency and safety of oil and gas development in permafrost. Moreover, the potential oil and gas leakage will damage the environment and the ecology of permafrost. Unfortunately, ice melting, formation subsidence, and wellhead behavior during this process have rarely been investigated in previous studies. In the present work, mechanical properties of permafrost were first experimentally investigated, which provided the basic parameter for subsequent numerical simulation. It was found that the ultimate strength gradually increased with the decreasing temperature, as well as the increasing confining pressure. Meanwhile, although the elastic modulus increased with decreasing temperature, it was less affected by confining pressure. Unlike other parameters, the Poisson’s ratio was hardly affected by temperature and confining pressure. Moreover, both the internal friction angle and the cohesion increased with decreasing temperature, but the influence degree varied within different temperature ranges. Then, ice melting, formation subsidence, and the instability behavior of the wellhead caused by the disturbance of the development operation were numerically explored. The investigation results show that the ice melting range in the reservoir section reached 8.06 m, which is much wider than that in other well sections. Moreover, failure of the cement–permafrost interface, caused by ice melting, resulted in a wellhead sinking of up to 1.350 m. Finally, the insulation effect of the vacuum-insulated casing showed that the temperature drop of the designed vacuum-insulated casing was much lower than that of the ordinary casing. When the fluid temperature within the wellbore was 70 °C, the temperature drop of the designed vacuum-insulated casing was 3.54 °C lower than that of the ordinary casing. This study provides support for maintaining wellhead stability during oil and gas extraction in permafrost for avoiding some environmental disasters (such as oil and gas leakage).

Slickline-Deployed Fiber-Optic Cable Provides First Production Profile for High-Temperature Gas Well

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 215512, “Slickline-Deployed Fiber-Optic Cable Provides First-Ever Production Profile for High-Temperature Gas Well,“ by Stuart Berry, SPE, Expro, and Danu Dirya, SPE, and Graeme Cowie, SPE, TotalEnergies, et al. The paper has not been peer reviewed. _ Distributed fiber-optic sensing (DFOS) allowed the continuous gathering of flow-profile information from a high-temperature, high-rate gas well. The objective of the case study described in the complete paper is to demonstrate that thermal inversion modeling can be used to produce a production-flow profile in an environment where conventional production logging is not possible. As a result of deploying DFOS, data can be acquired at more-realistic rates. Through performing of thermal inversion of distributed temperature sensing (DTS) data and analysis of distributed acoustic sensing (DAS) data, a more-accurate flow profile was achieved. Introduction Culzean is a high-pressure/high-temperature gas condensate field in the central North Sea. The main productive interval for the field is the Triassic Joanne sandstone deposited in a semiarid continental fluvial environment. The Jurassic Pentland sandstone deposited by meandering fluvial systems also contains significant resources. Initial reservoir pressure was 936 bar; the temperature was 170°C. The development consists of six production wells, five from the Joanne and one from the Pentland. While the reservoir interval is relatively thick, the depositional environment created a very layered reservoir with significant variability in reservoir quality. Flow-profile data over the reservoir has traditionally been acquired using production-logging tools with spinner velocity and pressure and temperature measurements. Production-log deployment can be problematic in high-rate wells, particularly when tubing is restricted because of pipe deformation or deposits in the tubing. In the Culzean field, several wells were selected for flow-profile monitoring. Previous slickline operations indicated that conventional production logging would be ineffective. Modeling showed significant tool-lift risk, meaning that the well could only be flowed at approximately 25% of its normal operating rate. A previous attempted production-logging campaign in the well resulted in no valid data acquisition but incurred a direct cost of $700,000 and a deferral of 10 days production estimated at a cost of $10.8 million. An alternative acquisition method was investigated to obtain production-profile data while minimizing risks associated with conventional production-log deployment. DFOS provides a continuous measurement over the entire length of the well for temperature and acoustic noise. A high-temperature slickline DFOS wire could allow Culzean well data acquisition under flowing conditions. Technology Selection Data acquisition was divided into a shut-in phase and a flowing phase. For the shut-in phase, a simplified production-logging toolstring was used to measure any crossflow over the reservoir section. The flowing phase would consist only of DAS data over the reservoir section, with a simple pressure/temperature memory tool in the sump of the well. The DFOS data would gather shut-in data before opening the well up to flow. For the conventional tool shut-in string, an inline caged spinner was selected.

Bottom sediments of the Shershnevskoye reservoir: Physicochemical characteristics and toxicity

The Shershnevskoye reservoir (ShR) is the main source of drinking water supply for the city of Chelyabinsk, which, since 2003, has been experiencing serious environmental problems caused by eutrophication processes. The purpose of this work was to study the bottom sediments (BS) of the ShR. BS were sampled in 4 locations of the ShR in the spring of 2024. We determined the 5 physicochemical parameters of the BS, the content of humic substances and gases (CO, CO2, CH4), 25 hydrochemical parameters and the toxicity of pore waters. It has been established that the bottom sediments of ShR are sandy silt, they have an average density of 1.008 g/cm3. In the longitudinal section of the reservoir, a trend towards an increase in the content of organic matter and methane in the BS from the upper reaches to the dam is observed. The pore waters belong mainly to the first (I) hydrochemical facies (Ca2+–Mg2+–Cl-–SO 2-) according to the Back (1961) classification. In the reservoir section, there is a clear trend of replacing bicarbonate ion with sulfate ion, and the concentration of chloride ion was minimal (from 0.1 to 1.1 mg/L). According to the results of biotesting using Scenedesmus quadricauda and Daphnia magna, all BS samples exhibit chronic toxicity, and two samples also exhibit acute toxicity, probably associated with the release of toxic products of organic matter mineralization.

Numerical solution of the problem of thermal effects on high-viscosity oil through a horizontal well

In this paper, the problem of developing a high-viscosity oil reservoir due to the effect of paragravity based on heating the reservoir section between the injection and production wells is considered. The thermal effect on the formation reduces the viscosity coefficient of the oil and increases the mobility of the raw material. The heat transfer equation is solved by the PSSS method. The task is solved in three stages. At the first stage, the oil reservoir is heated, at the second – its exposure, at the third - filtration.

True triaxial physics simulations and process tests of hydraulic fracturing in the Da’anzhai section of the Sichuan Basin tight oil reservoir

The limestone reservoir of the Da’anzhai section is the main production layer of Jurassic tight oil in central Sichuan, with tight and strongly heterogeneous reservoir rocks. In the early stages, small-scale plug removal and acidification techniques were mainly applied to the dacite section of the reservoir. However, using a single conversion method was not suitable for tight reservoirs with underdeveloped fractures. To address this challenge, we conducted large-scale real-world triaxial simulation test system experiments on hydraulic fracture propagation using samples from dense limestone outcrops. The aim was to elucidate the laws of hydraulic fracture propagation in dense limestone oil reservoirs. The L1 well in this area was selected to test the volumetric fracturing technology in order to achieve a breakthrough in test production and the reconstruction technology of the Da’anzhai section of the tight limestone reservoir. The experiments have shown that low stress differences, natural fracture development, and low viscosity slippery water are favorable factors for obtaining complex fracture morphology. In contrast to the construction parameters, the structural properties of the rock are the dominant factors in the formation of complex fracture morphologies. By optimizing the geological dessert and implementing targeted technological measures, bulk fracturing has been proven to be feasible for the dense limestone reservoir in the Da’anzhai section.

Economic Operation of Variable Speed and Blade Angle-Adjustable Pumping Stations of an Open-Channel Water Transfer Project

A large amount of energy would be consumed for open-channel water transfer projects due to the low efficiency of pumping stations. One measure to improve the efficiency of a pumping station is to install variable-frequency drives (VFDs). In this paper, a discharge optimization model is proposed for a single pumping station equipped with different numbers of variable speed and blade angle-adjustable pump (VSBAP) units, and then a head optimization model is proposed for cascade pumping stations. The study on the Miyun Reservoir Regulation and Storage Project in China shows that the installation of VFDs can increase the number of operable conditions of a single BAP unit by changing the blade angle and speed and ensure the high efficiency of the pumping unit under most operating conditions, thus reducing the energy consumption of the pumping station. It is desirable to install two VFDs in the Tuancheng Lake–Huairou Reservoir section to ensure the long-term operation of the cascade pumping stations in an economically profitable way. In conclusion, the installation of VFDs can effectively reduce the operation cost of cascade pumping stations.

Critical drawdown pressure prediction for sanding production of underground gas storage in a depleted reservoir in China

AbstractSanding production of the underground gas storage (UGS) in the depleted reservoir will cause the decline of effective storage capacity, and the erosion of well string and auxiliary equipment, and other engineering problems. A deep understanding of the sanding production contributes to maintaining the injection and production capacity of gas storage and the long‐term safety of the UGS. In this paper, core samples of five main sedimentary microfacies were drilled from the UGS in middle China. The mechanical properties with different conditions of the moisture content in multi‐cycling injection–production process were tested. The critical drawdown pressure (CDP) calculation methods for the UGS were established based on the stress analysis near the wellbore and the Mogi–Coulomb criterion. Adopting the finite element method simulation on the geological model of the target UGS, the geo‐stress of the formation was calculated by inversed analysis and validated based on the Kaiser effect of rock. Then, the CDP of two target wells of the UGS were investigated. The effects of the water moisture and the cycling times of the injection–production process on the CDP were also analyzed. The geo‐stress distribution shows that the horizontal maximum principal stress ranges from 53 to 68 MPa, and the horizontal minimum principal stress is 46–58 MPa in the target reservoir section, and the vertical minimum principal stress is 69–77 MPa in the target reservoir. The calculated CDP changed with the types of the sedimentary microfacies in the range of [6.27, 8.77] MPa, in which the CDP of the mixed mud and sand flat sedimentary facies was the lowest. The weakness of the CDP with the increasing of the moisture content and the cycling times were analyzed quantitively.

Production Forecasting of Unruly Geoenergy Extraction Wells Using Gaussian Decline Curve Analysis

Fast and rigorous well performance evaluation is made possible by new solutions of the pressure diffusion equation. The derived Gaussian pressure transient (GPT) solutions can be practically formulated as a decline curve analysis (DCA) equation for history matching of historic well rates to then forecast the future well performance and estimate the remaining reserves. Application in rate transient analysis (RTA) mode is also possible to estimate fracture half-lengths. Because GPT solutions are physics-based, these can be used for production forecasting as well as in reservoir simulation mode (by computing the spatial and temporal pressure gradients everywhere in the reservoir section drained by either an existing or a planned well). The present paper focuses on the physics-based production forecasting of so-called “unruly” wells, which at first seem to have production behavior noncompliant with any DCA curve. Four shale wells (one from the Utica, Ohio; one from the Eagle Ford Formation, East Texas; and two from the Wolfcamp Formation, West Texas) are analyzed in detail. Physics-based adjustments are made to the Gaussian DCA history matching process, showing how the production rate of these wells is fully compliant with the rate implied by the hydraulic diffusivity of the reservoir sections where these wells drain from.

Study Explores Integration of Subsea Optical Distribution Systems

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 32645, “All-Optical Subsea Sensing and Communications,” by Glenn Wilson, SPE, Halliburton, and Mauricio Uribe and Sigurd Moe, TechnipFMC, et al. The paper has not been peer reviewed. Copyright 2023 Offshore Technology Conference. Reproduced by permission. _ Subsea control systems use electric or optical communication channels within subsea optical distribution systems for redundant, duplex telemetry between topside facilities and subsea control systems. Downhole fiber-optic sensing (DFOS) systems use the same subsea optical distribution systems for establishing transmission paths between the same topside facilities and downhole sensing fibers. At the time of writing, subsea fiber-optic control and sensing systems have been operated on independent subsea optical distribution systems. This redundancy introduces complexity and cost into the overall subsea optical distribution system required for subsea developments. In the complete paper, the authors describe the systems that combine fiber-optic communications for subsea control systems and DFOS systems into the same subsea optical distribution system. Need for Systems Integration While maturity of, and demand for, DFOS technology has grown for offshore projects with dry-tree installations, operators have expressed the need for solutions to address fiber-optic technology gaps for subsea development projects. To this end, the topside DFOS interrogation of subsea wells requires optical engineering solutions to compensate for the insertion losses and back-reflections accumulated through umbilicals, multiple wet- and dry-mate optical connectors, splices, optical feedthrough systems (OFS), and downhole-sensing-fiber and optical wet-mate connectors (Fig. 1). To obviate these problems for distributed acoustic sensing (DAS), the authors previously introduced a subsea fiber topology with two transmission fibers from the topside to a remote optical circulator deployed in the optical flying lead (OFL) at the subsea tree. This limits the sensing fiber portion of the total fiber length to the fiber located below the remote circulator and eliminates all back-reflections from the multiple subsea connectors in the subsea infrastructure above the remote circulator. The DAS pulse-repetition rate is constrained only by the fiber length below the remote circulator, thus enabling dry-tree equivalent pulse-repetition rates (i.e., acoustic bandwidth) regardless of the tieback distance. This yields significant signal-to-noise ratio improvement through stacking and selective amplification while further enabling sensing of high-frequency acoustic events occurring inside, or in the vicinity of, the wellbore. The initial application for subsea DAS was installing fiber from the tubing hanger to the production packer for vertical seismic profiling. The ability to maximize acoustic bandwidth irrespective of tieback distance, however, enables a wider range of interventionless reservoir diagnostic applications. This has increased operator demand for installing fiber across the reservoir section.

Research on the improvement of wetted perimeter method and application in seasonal rivers-a case study of Fenhe River, China.

Environmental flow is vital for maintaining river ecosystem health and ensuring the normal growth of aquatic organisms. The wetted perimeter method is indeed very useful in the assessment of environmental flow due to consideration of stream forms and minimum flow for aquatic life habitat. In this study, a river with obvious seasonality and external water diversion was selected as the typical research object; taking Jingle, Lancun, Fenhe Reservoir, and Yitang hydrological sections as control sections, we improved the existing wetted perimeter method in three aspects: (1) We improved the selection of hydrological data series. The selected hydrological data series should be of a certain length and can well reflect the hydrological changes of wet, normal, and dry years. (2) Different from the traditional wetted perimeter method, which only gives one environmental flow value, the improved method calculates the environmental flow month by month. (3) The improved wetted perimeter method establishes the relationship between native fish survival and environmental flow. Results indicated that the improved wetted perimeter took the survival of the main fishes into consideration, the ratio of the calculated results by the slope method to the multi year average flow was greater than 10%, which can ensure the fishes' habitat is not being destroyed, and the results are more reasonable. Furthermore, the monthly environmental flow processes obtained were better than the annual unified environmental flow value determined by the existing method and are consistent with the natural hydrological situation and water diversion situation of the river. This study shows that the improved wetted perimeter method is feasible for research of river environmental flow with strong seasonal and large variation of annual flow.

3D VP, VS, and VP/VS Structures and Seismicity of the Lower Reaches of the Jinsha River, China

Abstract The Jinsha River flows through the tectonically active Sichuan and Yunnan regions, which have frequent strong earthquake activities. Four large-scale hydropower dams have been built in the lower reaches of the river and had begun impounding water successively since October 2012, with the Baihetan (BHT) and Xiluodu (XLD) being the second and fourth largest hydropower stations in the world. Using the seismic data recorded by dense seismic stations in the lower reaches of the Jinsha River from January 2010 to December 2019, we obtain the 3D crustal VP, VS, and VP/VS models and seismic relocations by applying the VP/VS model consistency-constrained double-difference tomography method (tomoDDMC). After Xiangjiaba (XJB) and XLD started to store water, earthquakes were mainly clustered in two areas where the seismicity was weak before the impoundment, that is, (1) the western segment of the Mabian-Yanjin fault (MBYJF) zone on the west side of the river and the tail section of XJB, and (2) the southwest part of Leibo-Yongshan basin near the middle section of XLD reservoir. We find that the areas where earthquakes are concentrated have characteristics of high-velocity and low-VP/VS. These particular features may provide important information for predicting the potential earthquake risk areas. In addition, we found a well-resolved high-velocity and low-VP/VS zone sandwiched between two layers of low velocity and high VP/VS at depths ranging from 3 to 10 km beneath the Qiaojia area along the Xiaojiang fault (XJF), which suggests that the seismic activity in this area may increase with the storage of the BHT dam in April 2021.

Characterization of a complex sand-rich gas hydrate reservoir system in the Indian marine continental margin with downhole log and seismic data

Logging-while-drilling (LWD) and coring data were acquired in Areas A, B, C and E during the National Gas Hydrate Program Expedition 02 (NGHP-02). At Sites NGHP-02-16, −17, −20, −23 and −24 of Area B in the Indian Krishna-Godavari Basin, the gas hydrate-bearing sand-rich reservoirs directly in contact with an underlying water-saturated sediment were revealed near the seismic-inferred bottom simulating reflector (BSR) along a large anticlinal structure. Lithofacies analysis of cores show that the lower gas hydrate-bearing reservoir section at these sites is an interbedded unit with thin fine-sand layers alternating with clay-rich layers. We reanalyzed the LWD data including resistivity, compressional-wave and shear-wave acoustic velocities to assess and compare the spatial variation of sand-hosted gas hydrate and possible related free-gas accumulations. The presence of free gas-bearing sediments in direct contact with gas hydrate-bearing sediments was confirmed at Sites NGHP-02-20 and −24 along the northeastern flank of the anticline. The sand-rich reservoirs associated with the Area B anticlinal feature reveal different pore-filling constituents and variable boundary conditions, including gas hydrate/water contacts and gas hydrate/free gas contacts. We infer that the sedimentary depositional history at Sites NGHP-02-20 and −24, may have resulted in an upward shift of the base of gas hydrate stability zone, that could have led to in situ gas hydrate dissociation and the accumulation of free gas and coexistence interval below the log-inferred gas hydrate-bearing reservoir sections. This study demonstrates that reservoir heterogeneity and fluid migration were major factors affecting the distribution of gas hydrate and free gas in the identified sand-rich reservoirs.

Rock physics and machine learning comparison: elastic properties prediction and scale dependency

Rock physics diagnostics (RPD) established based upon the well data are used to deterministically predict elastic properties of rocks from measured petrophysical rock parameters. However, with the recent advances in statistical methods, machine learning (ML) can help to build a shortcut between raw well data and rock properties of interest. Several studies have reported the comparison of rock physics and machine learning methods for the prediction of rock properties, but the scale dependence of the ML models was never investigated. This study aims at comparing the results from rock physics and machine learning models for predicting elastic properties such as bulk density (ρb), P-wave velocity (Vp), S-wave velocity (Vs), as well as Poisson’s ratio (v) and acoustic impedance (Ip) in a well from the Gulf of Mexico (GOM) in two different scale scenarios: the well log and seismic scales. The well data under examination was split into training and testing subsets to optimize and test the developed ML models. The RPD approach was also used to validate and compare the accuracy of predicted elastic properties. Backus averaging was later applied to upscale the well data to the seismic scale to examine the scale dependence and prediction accuracy of aforementioned physics-driven and data-driven approaches. Results show that RPD and ML methods provided consistent results at both well log and seismic scales, suggesting the scale independence of both approaches. Moreover, ML models showed better estimation of rock properties due to their “apparent” match with measured data at both scales compared to the RPD approach where a significant mismatch between measured and predicted rock properties was found in the reservoir section of the well. However, by conducting further quality control of the sonic data, it was found that the measured Poisson’s ratio was extremely high in the gas-saturated interval. Hence, the prediction from ML models in this particular case cannot be trusted as ML models were trained based on poor-quality well data with non-realistic Vs and v values. Such an issue, however, could be identified and corrected using RPD as presented in this study. We demonstrate the importance of incorporating domain knowledge, i.e., rock physics, to check data quality and validate results from data-driven models.

Engineering Approach Uses Underbalanced Coiled-Tubing Drilling

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 210978, “Novel Engineering Approach Using Underbalanced Coiled-Tubing Drilling Solutions for Tight Sour Gas Carbonate,” by Mohamed Osama Abd El Meguid, Ayman El Shahat, and Ali Sulaiman Bin Sumaida, ADNOC, et al. The paper has not been peer reviewed. _ Because of declining reservoir pressures in some of its onshore gas carbonate fields, the operator initiated a three-well underbalanced coiled-tubing drilling (UBCTD) campaign in its onshore Asab and Bab fields, with two wells to be drilled in Asab and one in Bab. Because of the high hydrogen sulfide (H2S) content, a closed-loop system—the first one successfully implemented in the Middle East, according to the authors—was implemented. The complete paper discusses the design and planning involved in the drilling of these three wells, the operational challenges encountered, and mitigations used. Introduction One of the operator’s main objectives was to increase production while safely maintaining or minimizing operating costs. One method of achieving these goals is the use of coiled tubing (CT) to drill formations in underbalanced mode. The Asab and Bab fields are southwest of Abu Dhabi. Both fields have high H2S and CO2 content, with a bottomhole temperature of approximately 260–270°F. The candidate wells were drilled conventionally until the top of the reservoir section; then, the UBCTD package was moved to drill the reservoir section in underbalanced mode. The typical well completions, from top to bottom, include the following: - 5.5-in. tubing - 4.5-in. tubing - 7-in. liner - 100 ft of 6-in. openhole Project Objectives Because of safety and logistical constraints, the project would use a closed-loop system and recirculate the drilling fluid, thus avoiding high water consumption. Also, the system needed to be designed to safely handle H2S in return fluids. UBCTD using a closed-loop system has been performed elsewhere but not in a high-H2S and high-CO2 environment. Trajectory Design and Tubing Forces Trajectory design is an important part of drilling operations; reservoir targets given by geologists and reservoir engineers must be met. To expose more drilling footage in producing formations and to increase overall productivity, the geologists provide formation-top coordinates so that the drilling engineer knows how to proceed as drilling progresses through the reservoir subunits. When the well trajectory was designed in the discussed case, the CT engineer input planned well surveys into software so that the CT forces could be analyzed. Because these predrilled wells had never had CT interventions, the friction coefficient was unknown and the outcome of the software could have been very different from that observed while drilling. Friction coefficients from other conventional CT operations within the UAE, as well as those from other CT drilling operations in the region, were reviewed and then used for analysis. With the lowest friction coefficient of 0.3 for open hole, the target drilling length could not be achieved. Project planning required a solution to enable the lateral to meet the proposed objectives.

Fundamentals of crystallization at oil-brine interfaces for conformance control and oil spill remediation applications

We have investigated the interfacial properties at a brine-hydrocarbon boundary with the prospect of understanding the crystallization process that takes place when certain electrolytes are present in the brine and when certain surfactants are present in the hydrocarbon phase. Solutions of nine cations and five carboxylic acids were investigated. We found that some combinations of electrolytes and acids than others are solidified at the brine-hydrocarbon interface. These interfacial phenomena were studied with an optical force tensiometer setup with a so-called buoyant droplet configuration. aim to utilize these specific interfacial formed crystals to design a method to form crystal plugs in high-flow sections (e.g., at fractures) of an oil reservoir. Ultimately, our studies target a real reservoir environment and we have included a range of different crudes with varying total acid numbers (TAN) and viscosities to bring the study a little closer to a realistic upstream setting. The electrolyte-surfactant combination that gives rise to the most clear-cut formation of crystals directly at the interface is involving Zn2+ or Cu2+ and dodecanoic acid (C11H23COOH). Several of the systems under study appears to be forming crystals within the hydrocarbon phase; these crystals are more likely a result of the surfactant-associated diffusive transfer of cations into the hydrocarbon phase with subsequent complexation. When it comes to the crudes, the findings are somewhat more complex, the acidity of the oil, not surprisingly, influences the interfacial properties including the crystallization propensity. The relationship between one-dimensional parameters such as TAN and crystallization propensity is not straightforwardly interpreted but it does seem like proper spiking can induce crystallization in most oils and that it is most favorably done in light oils where the diffusivity of the acids is largest. We have made the applicational space wider by also showing that the crystallization/interfacial phenomena can induce confinement of oil on a water surface; an observation that opens applications in oil spill remedies.

Simulation of wellbore temperature and heat loss in production well in geothermal site

ABSTRACT Knowledge of fluid flow temperature along the wellbore can be useful for a realistic calculation of the total heat production in geothermal wells. Therefore, wellbore modeling is an important part of the characterization of geothermal wells and predicting their future behavior. This study describes the dynamic transport of transient heat and fluid dynamic transport inside a geothermal well and also heat loss in the surrounding rocks. The objective of this investigation is to accurately predict temperature and pressure variations within the producing well GPK2 of the geothermal site Soultz-sous-Forêts. The temperature effect of possible leakage zones in the reservoir section of the production casing was also considered. A single-phase flow modeling was carried out using Comsol software. Our study highlights that the properties of the flow (well flow rates for steady and unsteady flow), of the fluid (density, viscosity, chemical composition), and the well (diameter, length, thermal properties of environments) are parameters, which directly influence the pressure and temperature profiles of the well. A sensitivity study has been carried out to demonstrate the role that these parameters play in the heat transport occurring in this well. According to our simulated results, during the flow of hot water in GPK2 well the production temperature of water decreases by dozen degrees of its downhole temperature. It is also shown that the leakage zone affects the temperature, decreasing it at least by 1–2°C.

Spatial and temporal variation of nearshore significant wave height in the Three Gorges Reservoir, China

The study of wave characteristic changes is critical for understanding the role of wave erosion in the shoreline erosion of reservoirs and its subsequent impact on environmental pollution. This study utilizes RBRvirtuoso D-wave-pressure-based wave gauges to make in situ observations of the nearshore significant wave height (SWH) in the Three Gorges Reservoir. The differential and impact factors affecting the SWH under varying water levels, in the main and tributary streams, and shoreline sections are analyzed. This research also investigates the alteration of the frequency distribution of the SWH. The findings indicate that the average SWH increases as the water level increases, reaching 1.2 cm, 1.5 cm, and 1.9 cm for water levels of 150 m, 165 m, and 175 m, respectively, with a SWH frequency distribution curve that becomes increasingly smooth. The average SWH in the mainstream is 2.9 times larger than that in the tributaries, with the former having a smoother frequency distribution curve. The average SWHs in different shoreline sections are inconsistent at the same water level, with the Badong (downstream) section near the Three Gorges Dam exhibiting a significantly higher average SWH than the Zhongxian (midstream) section further from the dam. When shipping activities intensify, there is often a marked increase in the magnitude of the SWH. The SWH in narrower reservoir sections is significantly greater than that in wider sections, with average measurements of 2.2 cm and 1.4 cm, respectively. Fluctuations of the water level, shipping activities, and other factors in the Three Gorges Reservoir have a significant impact on the alteration of the nearshore SWH, and changes in the SWH from low to high water levels may result in changes in both the spatial and temporal patterns of shoreline erosion. These alterations can, in turn, affect sediment and nutrient transport, potentially exacerbating environmental pollution issues.

Permanent Fiber-Optic DTS Evaluates Production Enhancement

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 31654, “Production Enhancement Evaluation Through Permanent Fiber-Optic Distributed-Temperature-Sensing Interpretation for a Gas-Lifted Producer in Field B, Offshore Malaysia,” by Chang Siong Ting, Nur’ain Minggu, and Dahlila Kamat, Petronas, et al. The paper has not been peer reviewed. Copyright 2022 Offshore Technology Conference. Reproduced by permission. _ In the complete paper, the authors evaluate the effectiveness of production-enhancement activities for Well B Long-String (i.e., Well BL) using distributed-temperature-sensing (DTS) technology. Installation of permanent fiber-optic cable across the reservoir sections has enabled gas-lift monitoring, identification of well-integrity issues, and zonal inflow profiling from perforation contribution. The effectiveness of executed remedial jobs is described along with findings and interpretations of DTS results. Field and Well BL Background Field B is a mature brownfield 45 km offshore east Malaysia in a water depth of approximately 230 ft. The field’s structure has a gentle rollover anticline with a collapsed crest caused by growth faulting. The reservoirs were deposited in a coastal shallow marine environment with channels. The production wells completed in these reservoirs were completed with internal gravel packs. The typical completion types for wells in Field B are dual strings with sliding sleeve doors (SSD), intended for commingled production from the multilayered reservoirs. Most of the wells in Field B were installed with permanent downhole gauges (PDGs), and five wells were equipped with permanent DTS across the reservoir section. The well was completed in 2015 as a gas-lifted dual-string producer with a 3½-in. completion string for short string (BS) and 3½×2⅞-in. tubing crossover for long string (BL). The long string of Well B also produces from two zones, Zones 2 and 3, while the short string of Well B produces from only one zone, Zone 1. Each zone consists of sublayers. In addition, DTS fiber-optic cable was installed along the long string across the reservoir sections in Well BL, and the system enabled the operator to monitor continuously the wellbore temperature across all producing intervals. Each zone also was equipped with a zonal PDG (temperature and pressure) and SSDs. DTS System The double-ended DTS system was installed permanently across the multilayered reservoir in Well BL to measure the dynamic change of temperature in the near-wellbore region over time. Double-ended temperature measurement was used to correct for differential light losses (light-loss correction) that appear gradually over the lifetime of the fiber as its quality is degraded because of hydrogen darkening or exposure to high temperatures. This measure improves the quality and accuracy of the measurement signal backscattered to the surface receiver for processing. With double-ended DTS, small thermal changes over time in the well can be tracked. Temperature measurements are detected in 1.6-ft intervals along the length of the cable. This generates a profile of temperature effects along the production string by analyzing backscattered Raman wavelength light from a pulsed laser source. This DTS measurement allows continuous monitoring of production events as they happen.

A Tiny-Fault Detection Strategy Based on Phase Congruency—An Example of Carbonate Reservoir in Ordos Basin, China

Tiny-fault detection plays a very important role in the research on the tight oil and gas reservoir in well area X in Ordos Basin, China. In this study, the target formation is the Majiagou dolomite reservoir section under the Ordovician salt with low-amplitude structures generally developed. The conventional attributes extracted from migrated seismic data could not achieve ideal results in detecting hidden faults with small displacement due to slight travel time differences and weak amplitude disturbances. To address this challenge, a segment and fusion strategy was adopted to highlight tiny faults in this region. First, the phase congruency analysis method was used to extract the local edges of coherence to locate the faults. Second, in the extraction process, the coherence was divided into segments according to the fault scales, and then enhanced segment by segment and fused. Third, the empirical formula of the new fault indicator was constructed by the phase congruency features, which can be used to accurately characterize tiny faults. This strategy performs well in both model tests and the migrated seismic data.