Reservoir Compartmentalization Research Articles

Production-Induced Subsidence at the Los Humeros Geothermal Field Inferred from PS-InSAR

Surface deformation due to fluid extraction can be detected by satellite-based geodetic sensors, providing important insights on subsurface geomechanical properties. In this study, we use Differential Interferometric Synthetic Aperture Radar (DInSAR) observations to measure ground deformation due to fluid extraction at the Los Humeros Geothermal Field (Puebla, Mexico). Our main goal is to reveal the pressure distribution in the reservoir and to identify reservoir compartmentalization, which can be important aspects for optimizing the production of the field. The result of the PS-InSAR (Persistent Scatterer by Synthetic Aperture Radar Interferometry) analysis shows that the subsidence at the LHGF was up to 8 mm/year between April 2003 and March 2007, which is small relative to the produced volume of5×106 m3/year. The subsidence pattern indicates that the geothermal field is controlled by sealing faults separating the reservoir into several blocks. To assess if this is the case, we relate surface movements with volume changes in the reservoir through analytical solutions for different types of nuclei of strain. We constrain our models with the movements of the PS points as target observations. Our models imply small volume changes in the reservoir, and the different nuclei of strain solutions differ only slightly. These findings suggest that the pressure within the reservoir is well supported and that reservoir recharge is taking place.

The role of avulsion and splay development in deep-water channel systems: Sedimentology, architecture, and evolution of the deep-water Pliocene Godavari “A” channel complex, India

Abstract Combined seismic images and core data from shallow gas-charged, deep-water sands in the western Bay of Bengal provide a detailed record of channel formation and evolution. The KG-D6 Block, western Bay of Bengal, includes two main Pliocene deep-water channel complex sets, termed the A and B complex sets, currently under gas production by Reliance Industries. These represent sinuous channels developed at the base of the delta slope off of the Godavari River and at the head of a long continental slope into the deep Bay of Bengal. The A complex set includes two main channel complexes, the older A150 and younger A100 channel complexes. The A complex provides an excellent opportunity to explore the geometry, sedimentation, and evolution of a small submarine channel system because of shallow reservoir depth, excellent 3D seismic coverage, availability of cores, and the nearly complete system-wide gas charge of the sandstones. Relict sea-floor topography and the processes of avulsion and splay development figure importantly in the overall evolution of slope channel systems. In the KG-D6 area, a sand-rich avulsion splay derived from an older channel complex became the template upon which the A channel complex set evolved. The component A150 and A100 channel complexes developed along a single sinuous course, with the channel complexes building through coupled channel erosion and coeval levee construction. The Godavari slope channels are not confined by scalloped valley walls and did not migrate laterally during their evolution. Mass transport deposits (MTDs) occur in all parts of the channel-fill section. The A100 channel complex displays a well-developed fining-upward cycle in most sections apparently not reflecting shifts in channel position or meander cuts offs, as inferred for some other deep-water channel systems, but rather through changes in the activity within the channels and through advances and retreats of frontal splays up and down the channel system. The Godavari data demonstrate the importance of avulsion and splay development in the evolution of deep-water sedimentary deposits, even high on passive margin slopes, which has implications for understanding the evolution of sinuous submarine channels and the development and distribution of hydrocarbon reservoir compartments.

Nucleation and Arrest of Dynamic Rupture Induced by Reservoir Depletion

AbstractSeismic events induced by the depletion of hydrocarbon reservoirs can cause damage to housing and cause societal and economic unrest. However, the factors controlling the nucleation and size of production‐induced seismic events are not well understood. Here we used geomechanical modeling of production‐induced stresses and dynamic rupture modeling to assess the conditions controlling down‐dip rupture size. A generic model of (offset) depleting reservoir compartments separated by a fault was modeled in 2‐D using the Finite Element package DIANA FEA. Linear slip‐weakening was used to control fault friction behavior. Fault reactivation was computed in a quasi‐static analysis simulating stresses during reservoir depletion, followed by a fully dynamic analysis simulating seismic rupture. The sensitivity of reactivation and rupture size to in situ stress, dynamic friction, critical slip distance, and reservoir offset was evaluated. After reactivation, a critical fault length was required to slip before seismic instability could occur. In a subsequent fully dynamic analysis the propagation and arrest of dynamic rupture was simulated. Rupture remained mostly confined to the reservoir interval but could also propagate into the overburden and underburden or sometimes transition into a run‐away rupture. Propagation outside the reservoir interval was promoted by a critical in situ stress, a large stress drop, a small fracture energy, and no or little reservoir offset. With increasing offset (up to the reservoir thickness), reactivation was promoted but dynamic rupture size decreased.

Using Bayesian Model Probability for Ranking Different Prior Scenarios in Reservoir History Matching

Summary This paper considers Bayesian methods to discriminate between models depending on posterior model probability. When applying ensemble-based methods for model updating or history matching, the uncertainties in the parameters are typically assumed to be univariate Gaussian random fields. In reality, however, there often might be several alternative scenarios that are possible a priori. We take that into account by applying the concepts of model likelihood and model probability and suggest a method that uses importance sampling to estimate these quantities from the prior and posterior ensembles. In particular, we focus on the problem of conditioning a dynamic reservoir-simulation model to frequent 4D-seismic data (e.g., permanent-reservoir-monitoring data) by tuning the top reservoir surface given several alternative prior interpretations with uncertainty. However, the methodology can easily be applied to similar problems, such as fault location and reservoir compartmentalization. Although the estimated posterior model probabilities will be uncertain, the ranking of models according to estimated probabilities appears to be quite robust.

Integrating geochemical and reservoir engineering approach to evaluate reservoir continuity: A case study from Foroozan field, Offshore Iran

Foroozan field, with seven different reservoir layers, is one of the complex fields in the Persian Gulf. The purpose of this study was to identify intra-reservoir compartmentalisation using geochemical and reservoir engineering evidences. On the basis of this approach, 11 gaseous samples, which belong to different wells producing from the Burgan reservoir of Foroozan field, were selected. Gas composition, gas isotopes and associated oil bulk properties were tested to determine the reservoir continuity through the Burgan reservoir. In addition, fluid contacts and properties are also used to investigate reservoir continuity. Regarding clear differences in gas composition such as hydrogen sulphide concentrations, at least two separate segments in the north and south of the reservoir were detected. Moreover, the percentages of the different gas components indicated two separate compartments. Other evidences such as \(\hbox {C}_{1}\)–\(\hbox {C}_{4}\) alkane isotopic compositions and sulphur and nitrogen isotopic signatures confirmed the Burgan reservoir compartmentalisation. A number of petroleum bulk properties confirmed gradual variations that provide supplementary evidence on the reservoir-filling direction, signifying that fluids equilibrium had not been extended through the Burgan reservoir, laterally. Initial reservoir condition, different original water–oil contacts, solution gas–oil ratio at original pressure and bubble point pressure are other reservoir engineering evidences that support the Burgan reservoir compartmentalisation.

Automatic fault detection in seismic data using Gaussian process regression

Compartmentalization of hydrocarbon reservoirs, change in fluid contacts, effects of high permeable fractures around faults, and hydrocarbon traps created by seal faults make fault detection and extraction as a necessity in the analysis of seismic data. Faulting disrupts the smoothness trend of geological layers (reflections in seismic sections) and displaces layers along its plane. Thus, a fault could be considered as an abnormal phenomenon that globally deviates normal behavior of layers around its plane. In the present study, faults are considered as sparse global anomalies in a seismic section that can be extracted using Gaussian process regression. The Gaussian process regression is a nonparametric probabilistic model based on Bayesian statistics that can be used to model spatial properties as a regression problem. The Gaussian process usually is used to extract and describe normal interactions from the data set using smooth functions.The main idea of this study is to detect the global anomaly using Gaussian process regression. For this purpose, we considered geological layers as smooth normal events in seismic sections. Therefore, the location of the fault plane is where the Gaussian process gets an error during describing the layers. Abnormalities such as faults cause the Gaussian process to suffer an error near the anomaly. We used these errors and analyzed them to detect probable locations of fault edge. Finally, we used a consistent connection algorithm to separate most probable fault points and to connect them to an edge using morphological reconstruction algorithm. The proposed algorithm was evaluated based on the receiver operating characteristics analysis. Several synthetic seismic sections with different levels of signal to noise ratios were used to evaluate the algorithm in the presence of random noise. The results showed that all points predicted by a diagnostic test fell into the area above the diagonal of the receiver operating characteristics space, which represents a good diagnostic classification.

Integrated electrokinetic processes for the remediation of phthalate esters in river sediments: A mini-review

Concerning the contamination of phthalate esters (PAEs) in river sediments, this mini-review introduces four recently reported novel “integrated electrokinetic (EK) processes” for the remediation purpose, namely two combined technologies of the EK process and advanced oxidation process (EK-AOP Processes) and two combined technologies of the EK process and biological process (EK-BIO Processes). The following is a comprehensive summary for these remediation processes: (1) the EK process coupled with nano-Fe3O4/S2O82− oxidation process – Test results have shown that nanoscale Fe3O4 played a significant role in activating persulfate oxidation. Even a recalcitrant compound like di(2‑ethylhexyl)phthalate (DEHP), its concentration in test sediment was reduced to 1.97 mg kg−1, far below the regulatory levels set by Taiwan EPA; (2) the EK process integrated with a novel Fenton-like process catalyzed by nanoscale schwertmannite (nano-SHM) – Test results have revealed that simultaneous injection of nano-SHM slurry and H2O2 into the anode reservoir and sediment compartment is a good practice. 70–99% in removal efficiency was obtained for various target PAEs; (3) enhanced in situ bioremediation coupled with the EK process for promoting the growth of intrinsic microorganisms by adding H2O2 as an oxygen release compound (ORC) – Test results have demonstrated that an intermittent mode of injecting lab-prepared ORC directly into the contaminant zone would be beneficial to the growth of intrinsic microorganisms in test sediment for in situ bioremediation of target PAEs; and (4) coupling of a second-generation ORC (designated 2G-ORC) with the EK-biological process – Test results have proved that 2G-ORC is long-lasting and can be directly utilized as the carbon source and oxygen source for microbial growth resulting in an enhanced biodegradation of PAEs. Except DEHP having a residual concentration of 4 μg kg−1, all other target PAEs in test sediment were totally removed by this novel combined remediation process.

Statistical analysis of historic hydrocarbon production data from Gulf of Mexico oil and gas fields and application to dynamic capacity assessment in CO2 storage

Numerical modeling of CO2 injection and reservoir flow is typically performed to forecast the number of wells, sustainable injection rates, and total storage volume (or mass). A critical determination for CO2 storage in depleted oil and gas reservoirs is characterization of reservoir compartmentalization which informs boundary conditions in simulating injection scenarios. Constraining boundary conditions during CO2 injection into geological formations is a key factor for feasible deployment project. Production history data from 616 wells in 100 oil and gas fields from Gulf of Mexico (GOM) offshore basin can be used to evaluate boundary conditions and total production (oil and gas) and therefor constrain the capacity for potential carbon storage. In general, the combination of decline curve analysis and statistical analysis (to specify constraining boundary conditions) allows the determination of the range of reservoir performance if existing inactive production wells in GOM area of study are used reversibly for CO2 injection.To constrain the mass of CO2 which can be injected, it is useful to consider estimates of cumulative bulk (hydrocarbon + brine) production (CBP), which can be converted to equivalent CO2 mass considering reservoir conditions. Summary CBP statistics are presented as a probability of non-exceedance (PNE), providing a forecast of likely injection rates and masses for other located CO2 storage projects with similar geology and boundary conditions in the future. The 50% PNE for Equivalent CO2 is a novel quantitative approach to investigate the possible injection capacity in CO2 storage projects. The PNE sensitivity analysis shows that reservoir age, drive mechanism, reservoir trap, and reservoir porosity are the key controlling parameters for productivity and consequently optimum CO2 storage capacity. Another key finding is the negligible correlation between CBP with reservoir transmissivity and porosity, which implies that other factors than just petrophysical parameters should be studied as constraining factors for CO2 storage statistical analysis.

A State-of-the-Art Literature Review on Capacitance Resistance Models for Reservoir Characterization and Performance Forecasting

Capacitance resistance models (CRMs) comprise a family of material balance reservoir models that have been applied to primary, secondary and tertiary recovery processes. CRMs predict well flow rates based solely on previously observed production and injection rates, and producers’ bottomhole pressures (BHPs); i.e., a geological model and rock/fluid properties are not required. CRMs can accelerate the learning curve of the geological analysis by providing interwell connectivity maps to corroborate features such as sealing faults and channels, as well as diagnostic plots to determine sweep efficiency and reservoir compartmentalization. Additionally, it is possible to compute oil and water rates by coupling a fractional flow model to CRMs which enables, for example, optimization of injected fluids allocation in mature fields. This literature review covers the spectrum of the CRM theory and conventional reservoir field applications, critically discussing their advantages and limitations, and recommending potential improvements. This review is timely because over the last decade there has been a significant increase in the number of publications in this subject; however, a paper dedicated to summarize them has not yet been presented.

Integration of Precipitation Kinetics From an In Vitro, Multicompartment Transfer System and Mechanistic Oral Absorption Modeling for Pharmacokinetic Prediction of Weakly Basic Drugs

Solubility, dissolution, and precipitation in the gastrointestinal tract can be critical for the oral bioavailability of weakly basic drugs. To understand the dissolution and precipitation during the transfer out of the stomach into the intestine, a multicompartment transfer system was developed by modifying a conventional dissolution system. This transfer system included gastric, intestinal, sink and supersaturation, and reservoir compartments. Simulated gastric fluid and fasted state simulated intestinal fluid were used in the gastric and intestinal compartment, respectively, to mimic fasted condition. The new transfer system was evaluated based on 2 model weak bases, dipyridamole and ketoconazole. Traditional 2-stage dissolution using 250 mL of simulated gastric fluid media, followed by 250 mL of fasted state simulated intestinal fluid, was used as a reference methodology to compare dissolution and precipitation results. An in silico model was built using R software suite to simulate the in vitro time-dependent dissolution and precipitation process when formulations were tested using the transfer system. The precipitation rate estimated from the in vitro data was then used as the input for absorption and pharmacokinetic predictions using GastroPlus. The resultant simulated plasma concentration profiles were generally in good agreement with the observed clinical data, supporting the translatability of the transfer system in vitro precipitation kinetics to in vivo.

RESERVOIR COMPARTMENT ASSESSMENT: A CASE STUDY OF BANGKO AND BEKASAP FORMATION, CENTRAL SUMATRA BASIN INDONESIA

The reservoir compartment assessment for a case study of the Agur field, Central Sumatra Basinhas been successfully carried out by using fault seal analysis (FSA). The objective of this paper is to assessubsurface fault properties in term of the fault sealing that was defining the hydrocarbon reservoir compartment.In this work, the FSA was performed by integrating juxtaposition, shale gouge ratio (SGR) and transmissibilityanalysis over fault plane that was identified within reservoir layers on the Bangko and Bekasap formation. Thejuxtaposition seal is intended to assess how the reservoir layer is juxtaposed across the fault plane over eitherreservoir or non-reservoir layer. The SGR analysis is applied to estimate the shale content in the fault plane,which is caused by the fault movement of sequence stratigraphy. The last analysis of transmissibility is carriedout to calculate the capacity of a reservoir to drain the hydrocarbon through a fault plane. Faults architecture(throw, heave, and orientation) and the reservoir layer target were identified based on 3D seismic and well logdata interpretation. The FSA is applied to nine faults that formed nine reservoir compartments within threereservoir layers, which are obtained from 3D seismic and well log interpretation. The fault characteristics wereclassified and the fault seal distribution map was produced to identify the reservoir connectivity among the faults.The FSA results show that nine identified compartments in the first reservoir layer are clustered into fivecompartments. In addition, the FSA clustered nine identified compartments in the second reservoir layer intofour compartments. In contrast, nine compartments in the third reservoir layer were connected each other thatare clustered into one compartment. These results are useful not only for evaluating future hydrocarbon traps butalso for future field development.

Integration of 3D-seismic and petrophysical analysis with rock physics analysis in the characterization of SOKAB field, Niger delta, Nigeria

Compartmentalization of reservoirs and technical failures experienced in data acquisition, processing and interpretation, without doubt, hinder the effective characterization of reservoirs. In this research, to ensure accuracy, three methods were integrated to characterize reservoirs in SOKAB field. Petrophysical analysis, seismic interpretation, and modeling, and rock physics analysis were utilized. Its objectives were: to develop a template to facilitate improvements in future reservoir characterization research works and producibility determination; to utilize rock physics models to quality check the seismic results and to properly define the pore connectivity of the reservoirs, and to locate the best productive zones for future wells in the field. Forty-three faults were mapped and this included five major faults. Two hydrocarbon bearing sand units (A & B) were correlated across five wells. Structural maps were generated for both reservoirs from which majorly fault assisted and dependent closures were observed. The petrophysical analysis indicated that the reservoirs have good pore interconnectivity (Average Фeffective = 23% & 22% and Kaverage = 1754md & 2295md). The seismic interpretation and modeling alongside the petrophysical analysis were then quality checked via qualitative rock physics analysis. From the Kdry/Porosity plot, the sands were generally observed to lie within the lower Reuss and upper Voigt bound which indicates a low level of compaction. From the velocity–porosity cross plot, it was revealed that the lower portions of the reservoirs were poorly cemented and this could hinder their producibility.

Fused spectral-decomposition seismic attributes and forward seismic modelling to predict sand bodies in meandering fluvial reservoirs

Abstract Understanding the hierarchical architectural elements of fluvial sand bodies is important for planning their development strategy and to enhance oil recovery. Red-Green-Blue (RGB) blending of multiple seismic attributes and forwarding seismic modelling are commonly used in the analysis of compound sand bodies. However, RGB blending of multiple seismic attributes can only qualitatively describe the boundaries and thickness of sand bodies. The forward seismic modelling techniques previously documented in the literature are not effective when depicting the geometry of, and stacking relationships between, sand bodies (i.e., reservoir compartmentalisation). Hence, we propose in this work a new workflow that combines fused spectral-decomposition seismic attributes (SDSAs) and forwarding seismic modelling to quantitatively predict sand thickness, and to characterise stacking relationships between sand bodies. First, we employ a Support Vector Machine (SVM) algorithm to fuse high, middle, and low frequency components (attributes) of seismic data so as to quantitatively predict the thickness of sand bodies. Second, we define the seismic waveform response patterns corresponding to the typical conceptual stacked sand bodies. With the constraints of waveform patterns and predicted sand thickness (fused SDSAs), the geometry and stacking relationships of the sand bodies are characterised by forward seismic modelling. To illustrate the effectiveness of our proposed workflow, we apply it to the Neogene Minghuazhen Formation (Nm) of the QHD 32–6 oil field, Bohai Bay Basin, China. We define five architectural elements of a meandering fluvial reservoir by analysing the hierarchy of sand bodies using our workflow. The predicted sand bodies in this workflow were further proven by horizontal drilling and production data.

Chimeric antigen receptor T-cell approaches to HIV cure.

Combination antiretroviral therapy (ART) has enabled tremendous progress in suppressing HIV replication in infected patients. However, ART alone cannot eradicate HIV and its latent, persisting reservoirs. Novel approaches are needed to eradicate the virus or achieve functional cure in the absence of ART. Adoptive T-cell therapies were initially tested in HIV-infected individuals with limited efficiency. Benefiting from new and improved methodologies, an increasing array of CAR T-cell therapies has been successfully developed in the cancer immunotherapy field, demonstrating promising new avenues that could be applied to HIV. Numerous studies have characterized various HIV-specific CAR constructs, types of cytolytic effector cells, and CAR-expressing cells' trafficking to the reservoir compartments, warranting further in-vivo efforts. Notably, the ability of CAR cells to persist and function in low-antigen environments in vivo, that is, in ART-suppressed patients, remains unclear. Despite promising results in preclinical studies, only a handful of clinical trials have been initiated worldwide. Several obstacles remain prior to successful application of HIV-specific CAR T-cell therapies in patients. In this review, we survey the current state of the field, and address paths towards realizing the goal of an efficacious HIV CAR T-cell product.

Erosion and ponding of Thunder Horse deepwater turbidites by mass transport complexes in Mississippi Canyon based on image log sedimentology

Abstract Mass transport complexes are often associated with deepwater turbidite reservoirs, but typical subsurface data sets are of insufficient resolution or coverage to determine if and how the mass transport complexes have an impact on reservoir architecture. We present a case study of integrated, high resolution data (core, image logs, and seismic) from Thunder Horse, one of the largest deepwater oil and gas discoveries in the Gulf of Mexico, to illustrate how mass transport complexes can both compartmentalize and pond reservoirs. The key data type enabling these conclusions are image logs, which reveal erosive mass transport complexes whose emplacement removed the upper portion of one of the Thunder Horse sandstone reservoirs on the northwest side of the asset and resedimented the sand as multiple smaller compartments. Stacked seafloor landslide deposits interbedded with turbidite sandstone reservoirs are herein characterized in detail from image logs at Thunder Horse, located in lower Mississippi Canyon. Dips from bedding boundaries on image logs in the sandstone reservoirs show little variation in structural tilt ( Unconformable bedding contacts at the tops of the sandstone reservoirs in northern Thunder Horse suggest scouring and erosion, whereas basal sandstone contacts are in conformance with overall structural dip, suggesting amalgamation. On seismic data, the mass transport complexes stack and mound together, forming a paleo-topographic high with at least 30 m of relief. Core acquired in this mudrock-dominated deposit reveals convoluted and folded bedding capped by 0.5 m of highly bioturbated marl that is interpreted as a Glossifungites hiatal surface. The implication is that the mass transport complexes formed a topographic obstacle that diverted subsequent debris and turbidite flows, and later created localized ponding and thickening of the overlying reservoir. Thus, mass transport complexes were found to both erode and augment sandstone reservoirs. Biostratigraphic dating of the two reservoirs brackets their deposition as occurring in As a case study this type of integrated, high resolution data has wide applicability to other deepwater, sub-salt reservoirs, as improved structural and depositional interpretations inform reservoir performance and impact future well plans. Further, recognition of mass transport complexes as agents of reservoir compartmentalization and sandstone ponding allows for more accurate reserves estimation.

Seismic analysis of the igneous intrusions in the Ash Shaer Area in the Northern Palmyrides, Syria and their impacts on petroleum system

The increasing availability of 3D seismic data and well logs from Ash Shaer Area has provided fundamental new insights into the Miocene igneous activity and its impacts on the petroleum system. The well logs, time slices, seismic attributes, and the seismic sections formed effective tools in delineating the igneous intrusions in the study area. Due to distinct geophysical property contrasts with host rocks (e.g., higher Vp, density, and resistivity than host rocks), intrusions were easily delineated on the well logs and then on the seismic data. The detailed analyses of 3D seismic data have provided valuable insights into the (1) interaction between strike-slip faults and igneous intrusion, (2) reservoir compartmentalization, and (3) geological risk in hydrocarbon exploration. Our analysis explained the bad reservoir properties (porosity and permeability) in some parts of the study area, which in turn explained why one of the drilled wells was a dry well. As a result of this study, a map of geological risk in hydrocarbon exploration and a schematic model of the reservoir formation in the Miocene have been generated.

Follicular CD4 T Helper Cells As a Major HIV Reservoir Compartment: A Molecular Perspective.

Effective antiretroviral therapy (ART) has prevented the progression to AIDS and reduced HIV-related morbidities and mortality for the majority of infected individuals. However, a lifelong administration of ART is necessary, placing an inordinate burden on individuals and public health systems. Therefore, discovering therapeutic regimens able to eradicate or functionally cure HIV infection is of great importance. ART interruption leads to viral rebound highlighting the establishment and maintenance of a latent viral reservoir compartment even under long-term treatment. Follicular helper CD4 T cells (TFH) have been reported as a major cell compartment contributing to viral persistence, consequent to their susceptibility to infection and ability to release replication-competent new virions. Here, we discuss the molecular profiles and potential mechanisms that support the role of TFH cells as one of the major HIV reservoirs.

How, where, and when do radial faults grow near salt diapirs?

We examine 3-D seismic reflection data from the Santos Basin, offshore Brazil to determine how, where and when do radial faults grow near a sub-circular salt diapir (stock). We show roof stretching alone cannot account for the large heights and lengths of the kilometre-scale radial faults, suggesting stock widening (‘stem push’), a mechanism implied in numerical models but not yet documented in natural examples, played a pivotal role in radial fault formation. We suggest that, when a diapir is covered by a roof, radial faults form in its overburden due to roof stretching, extending no further than the limit of the drape folding. The roof may then be shouldered aside and the faults buried along the stock flanks, exposing these strata to stem push-related stresses that may then reactivate pre-existing or form new radial faults. Radial faults, irrespective of how they formed, may dip-link with or offset one-another as salt continues to rise. We suggest the causal mechanism for radial fault formation will likely change as roof thickness varies during diapirism, with this reflecting the ratio between sedimentation rate and salt volumetric flux. Our findings are likely applicable to other diapirs, helping us not only to interpret the paleo-stress state of salt-bearing sedimentary basins, but also advancing our understanding of fracture distributions, potential fluid flow pathways, and reservoir compartmentalization around salt diapirs in basins where seismic reflection imaging is poor.

Architecture and reservoir quality of low-permeable Eocene lacustrine turbidite sandstone from the Dongying Depression, East China

Abstract The architecture and quality of lacustrine turbidites that act as petroleum reservoirs are less well documented. Reservoir architecture and multiscale heterogeneity in turbidites represent serious challenges to production performance. Additionally, establishing a hierarchy profile to delineate heterogeneity is a challenging task in lacustrine turbidite deposits. Here, we report on the turbidites in the middle third member of the Eocene Shahejie Formation (Es3), which was deposited during extensive Middle to Late Eocene rifting in the Dongying Depression. Seismic records, wireline log responses, and core observations were integrated to describe the reservoir heterogeneity by delineating the architectural elements, sequence stratigraphic framework and lithofacies assemblage. A petrographic approach was adopted to constrain microscopic heterogeneity using an optical microscope, routine core analyses and X-ray diffraction (XRD) analyses. The Es3m member is interpreted as a sequence set composed of four composite sequences: CS1, CS2, CS3 and CS4. A total of forty-five sequences were identified within these four composite sequences. Sand bodies were mainly deposited as channels, levees, overbank splays, lobes and lobe fringes. The combination of fining-upward and coarsening-upward lithofacies patterns in the architectural elements produces highly complex composite flow units. Microscopic heterogeneity is produced by diagenetic alteration processes (i.e., feldspar dissolution, authigenic clay formation and quartz cementation). The widespread kaolinization of feldspar and mobilization of materials enhanced the quality of the reservoir by producing secondary enlarged pores. In contrast, the formation of pore-filling authigenic illite and illite/smectite clays reduced its permeability. Recovery rates are higher in the axial areas and smaller in the marginal areas of architectural elements. This study represents a significant insight into the reservoir architecture and heterogeneity of lacustrine turbidites, and the understanding of compartmentalization and distribution of high-quality sand reservoirs can be applied to improve primary and secondary production in these fields.

Mitigating induced seismicity around depleted gas fields based on geomechanical modeling

Mitigation of induced seismicity associated with large-scale energy production from subsurface resources requires models beyond the current state of the art. In countries with long histories of conventional gas production, such as the Netherlands, issues are mainly associated with depletion-induced seismicity caused by fault reactivation due to differential compaction of reservoir compartments that are juxtaposed at faults. Geomechanical modeling approaches can be extended and integrated to better assess the occurrence of depletion-induced seismicity and provide a basis to modify operations with the aim of mitigating seismicity. Static models of fault stability and reactivation can be used to analyze the location and likelihood of fault reactivation during injection or depletion operations. Dynamic models of fault rupture and seismic wave propagation can be used to analyze the characteristics of induced seismicity from seismic source to expressions (motions) at surface or potential sensor locations. Ensemble-based optimization workflows can be used to maximize production under constraints imposed by thresholds for induced seismicity. The combination of these modeling approaches can be used to determine fault sections that are most prone to induce seismicity, analyze the fault rupture process and associated characteristics of induced seismicity, and optimize well production strategies for minimizing induced seismicity. Integrated geomechanical modeling of depletion-induced seismicity and production optimization workflows can lead to gas production strategies that maximize total gas production while minimizing seismic risk.