High Permeability Zones Research Articles

Microscopic remaining oil initiation mechanism and formation damage of CO2 injection after waterflooding in deep reservoirs

Injecting CO2 into deep reservoirs with high temperature and pressure (HTHP) is a promising method for enhancing oil recovery (EOR) and CO2 utilization and storage (CUS). It is, however, challenging to quantitatively unravel the initiation mechanisms of micro-remaining oil and formation damage using microfluidic technology at 115 °C and 55 MPa. In this study, water/gas flooding experiments in the micromodel has carried out on the HPHT microfluidic experimental platform. The results reveal that 35.41% of the micro-remaining oil is recovered by scCO2 extraction on the funnel-shaped interface, and 11.21% by carbonated water swelling. When water is injected into heterogeneous reservoirs, the oil-water displacement front in the high-permeability zone is less stable than that in the low-permeability zone. Subsequent scCO2 injection resulted in asphaltene deposits (approximately 10.49% of pore volume), including low-velocity deposition, corner deposition and trap deposition, which reduced reservoir permeability. Moreover, compared with continuous CO2 injection, the asphaltene deposition is reduced by 4.25% of CO2 injection after waterflooding, including 2.64% in the high-permeability zone and 1.61% in the low-permeability zone. These observations provide important theoretical support for the application of CO2-EOR technology and carbon storage in deep reservoirs.

Silicification, flow pathways, and deep-seated hypogene dissolution controlled by structural and stratigraphic variability in a carbonate-siliciclastic sequence (Brazil)

Fractured and karstified carbonate units are key exploration targets for the hydrocarbon industry as they represent important reservoirs. Furthermore, large water reserves and geothermal systems are hosted in carbonate aquifers. This paper documents the relationships between stratigraphy, structural patterns, silicification, and the spatial-morphological organization of a 3D multistorey cave system developed in a Neoproterozoic mixed carbonate-siliciclastic sequence. We found that the combination of lithology, silicification, fracture patterns (controlled by lithostratigraphic variability), and petrophysical properties control the formation of high or low permeability zones; their distribution was fundamental for the spatial organization of dissolution and the compartmentalization of the resulting conduit system in different speleogenetic storeys. We propose a deep-seated hydrothermal origin for the fluids involved in the main phases of karst formation. Warm and alkaline hydrothermal fluids caused silica dissolution, followed by chalcedony and quartz reprecipitation in pore space and fractures. Rising fluids concentrated along through-going vertical fracture zones in the lower storey, whereas sub-horizontal bedding-parallel fluid flow was focused on sedimentary packages containing highly silicified dolostones (SiO2>80 wt%) characterized by high permeability. The Calixto Cave is an enlightening example for the complex speleogenetic history affecting a mixed carbonate-siliciclastic succession where the combined effect of silicification and hydrothermal karst dissolution can potentially generate high-quality reservoirs.

Conformance control by a microgel in a multi-layered heterogeneous reservoir during CO2 enhanced oil recovery process

Injecting CO2 into the underground for oil displacement and shortage is an important technique for carbon capture, utilization and storage (CCUS). One of the main problems during the CO2 injection is the channeling plugging. Finding an effective method for the gas channeling plugging is a critical issue in the CO2 EOR process. In this work, an acid-resistance microgel named dispersed particle gel (DPG) was characterized and its stability was tested in the CO2 environment. The microgel size selection strategies for the homogeneous and heterogeneous reservoirs were respectively investigated using the single core flooding and three parallel core flooding experiments. Moreover, the comparison of microgel alternate CO2 (MAC) injection and water alternate CO2 (WAC) injection in the dual core flooding experiments were presented for the investigation of the role of microgel on the conformance control in CO2 flooding process. The results have shown that the microgel featured with NH and CN groups can keep its morphology after aging 7 days in the CO2 environment. Where, the small microgel with unobstructed migration and large microgel with good plugging efficiency for the high permeability zone were respectively featured with the higher recovery factor in homogeneous and heterogeneous conditions, which indicate they are preferred used for the oil displacement and conformance control. Compared to WAC injection, MAC injection had a higher incremental recovery factor of 12.4%. It suggests the acid-resistance microgel would be a good candidate for the conformance control during CO2 flooding process.

A new predrilling reservoir permeability prediction model and its application

The accurate prediction of sandstone permeability from variables such as porosity, composition, and texture is one of the major problems in petroleum geology. However, the application of geological variables related to diagenesis in permeability prediction models is relatively rare, especially the anomalous variations of clay content and type. This study investigates the differential control of sedimentation and diagenesis on permeability using a comprehensive analysis of cores, thin sections, routine core analysis, X-ray diffraction, and scanning electron microscopy from sandstone samples in the third member of the Weizhou Formation (Ew3), Weizhou 12-X oilfield, Weixinan Sag, Beibu Gulf Basin, China. An innovative sandstone reservoir permeability prediction model is proposed by introducing the clay factor β confining the effect of clay minerals on permeability, predicting the spatial distribution of diagenetic index (ID) using the Diagenetic Modeling System (DMS), and improving the Walderhaug permeability prediction model. The permeability of the well evaluated in the study was predicted with the relative and absolute errors changing from 0.01 mD to 192.65 mD and from 0.00 to 1.00, with an average values of 38.6 mD and 0.33, respectively, based on the sandstone reservoir permeability prediction model in Ew3. The permeability predicted by the permeability prediction model matches well with the measured permeability in Ew3. The results indicate that permeability is successfully predicted by the modified Walderhaug permeability prediction model for most sandstone reservoirs with strong diagenesis (such as anomalous changes in clay mineral types and content) under the background of a single distributary channel sedimentary microfacies. In general, anomalously high permeability zones are preferentially distributed in dominant sedimentary-diagenetic facies.

Laboratory Studies for Design of a Foam Pilot for Reducing Gas Channeling from Gas Cap in Production Well in Messoyakhskoye Field

Summary This paper highlights the difference between foam injection for gas blocking in production well and injection well and emphasizes the use of polymer enhanced foam. Moreover, this paper shows systematic experimental methods for choosing suitable foam systems for gas blocking in production well considering different factors, which provides a guide regarding what kinds of foaming agents and polymer stabilizers should be used and how to evaluate them for designing a pilot application. The target in this work is the Vostochno-Messoyakhskoye field, operated by Gazpromneft, which is currently experiencing gas channeling from the gas cap in production wells because of strong heterogeneity. Foam has long been considered as a good candidate for gas blocking. However, foam injection for gas blocking in production wells is different from that in injection wells, which requires a long-term impact on gas-saturated highly permeable areas without significantly affecting the phase permeability of oil in the reservoir. Therefore, for gas blocking in production well, a long half-life time of foam is required to sustain stable foam because a continuous shear of surfactant solution/gas cannot be achieved as in injection wells. Thus, reinforced foam by polymer (polymer-foam) is chosen. Four polyacrylamide polymer stabilizers and five anionic surfactants were evaluated using bulk test to determine foaming ability, foam stability, and effect of oil by comparing foam rate and half-life time to determine the suitable foam system with optimal concentrations of reagents. Furthermore, filtration experiments were conducted at reservoir conditions to determine the optimal injection mode by evaluating apparent viscosity, breakthrough pressure gradient, resistance factor, and residual resistance factor. Polymer can significantly improve half-life time (increase foam stability), and the higher the polymer concentration, the longer the half-life time. But simultaneously, a high polymer concentration will increase the initial viscosity of the solution, which not only decreases the foam rate but also increases difficulties in injection. Therefore, an optimal polymer concentration of about 0.15–0.2 wt% is determined considering all these influences. Filtration experiments showed that the apparent viscosity in the core first increased and then decreased with foam quality (the volumetric ratio of gas to total liquid/gas flow). The optimal injection mode is coinjection of surfactant/polymer solution and gas to in-situ generate foam at the optimal foam quality of about 0.65. Filtration experiments on the different permeability cores showed that the gas-blocking ability of polymer-foam is better in high-permeability cores, which is beneficial for blocking high-permeability zone. It should also be noted that under a certain ratio of oil-to-foam solution (about lower than 1 to 1), the presence of high-viscosity crude oil slowly decreased the foam rate with increasing oil volume, but significantly increased the half-life time (i.e., foam stability which is favorable for foam treatment in production well).

Characteristics of gas–water flow during gas injection in two-dimensional porous media with a high-permeability zone

A marginal gas injection method was previously proposed based on two-dimensional (2-D) homogeneous porous media, and the feasibility of isolating the oil shale pyrolysis zone from the surrounding hydrological environment had been demonstrated. The gas–water flow characteristics and dynamics during gas injection in 2-D porous media with a high-permeability zone (HPZ) were studied further based on the presence of a HPZ after fracturing oil shale reservoirs. A series of experiments were performed when the gas-injection point was located outside, at the boundary, or inside the HPZ (Case1-3). The HPZ enriched the injected gas, and in Cases 2 and 3, the gas inside the HPZ permeated to the low-permeability zone (LPZ) on both sides, forming two wing tributaries. However, in Case 1, water flowed into the HPZ in the opposite direction. In Cases 2 and 3, the direction of the local pressure gradient on both sides of the HPZ was completely opposite, indicating that the distribution of the pressure field was the direct cause of the gas–water flow characteristics. Therefore, the water-stopping effect of gas injection is primarily reflected in the HPZ. Additionally, the effect was best when the gas-injection point was set at the boundary or inside of the HPZ. These results were verified using reservoir-scale simulations and tests, in which the water yield decreased to ∼ 100 kg/d. Subsequently, we recommended the sites of gas-injection wells for water stopping. All results are expected to provide strategies and theories for dealing with the adverse hydrological environment in large-scale oil shale in situ exploitation.

Active structures and thermal state of the Piton de la Fournaise summit revealed by combined UAV magnetic and thermal infrared measurements

In this study, we demonstrate the strong potential of combining Unmanned Aerial Vehicle (UAV)-based thermal infrared (IR) and magnetic measurements to image the thermal state of volcanic edifices, as well as the distribution of active volcano-tectonic features at depth. Since magnetization is strongly dependent on temperature and alteration, thermally active structures are also associated with a decrease in magnetization. Based on the analysis of recent combined magnetic and infrared acquisitions, we focus on the recent evolution of the summit activity at Piton de la Fournaise. The comparison clearly highlights zones of major thermal activity, alteration and high permeability, and potentially areas of low mechanical resistance. Those observations provide information on preferential pathways for future activity, and also provide constraints on fluid transfer, diffusion, and cooling processes occurring within the volcano subsurface. Through reiterations, such combined UAV measurements are therefore particularly relevant in monitoring volcanic hazards before, during and after eruptions.

Active structures and thermal state of the Piton de la Fournaise summit revealed by combined UAV magnetic and thermal infrared measurements

In this study, we demonstrate the strong potential of combining Unmanned Aerial Vehicle (UAV)-based thermal infrared (IR) and magnetic measurements to image the thermal state of volcanic edifices, as well as the distribution of active volcano-tectonic features at depth. Since magnetization is strongly dependent on temperature and alteration, thermally active structures are also associated with a decrease in magnetization. Based on the analysis of recent combined magnetic and infrared acquisitions, we focus on the recent evolution of the summit activity at Piton de la Fournaise. The comparison clearly highlights zones of major thermal activity, alteration and high permeability, and potentially areas of low mechanical resistance. Those observations provide information on preferential pathways for future activity, and also provide constraints on fluid transfer, diffusion, and cooling processes occurring within the volcano subsurface. Through reiterations, such combined UAV measurements are therefore particularly relevant in monitoring volcanic hazards before, during and after eruptions.

Effects of thief zones on displacement efficiency: Microfluidic pore-scale and conformance control analysis

Thief zones are regions with high permeability, usually formed in mature or depleted reservoirs after water flooding, which can further reduce the overall recovery during subsequent EOR stages. While existing conformance control solutions alleviate the impact of thief zones, selecting an optimal solution based on current laboratory methods is challenging, since current methods fail to isolate the impact of thief zones, lack tight control of initial conditions, and use long evaluation times as well as large sample volumes. In this study, a microfluidic analogue is designed and fabricated with multiple permeability regions, representing thief zones in a reservoir, to evaluate the performance of polymer flood in a porous medium. The analogue contains four connected and distinct heterogenous zones of different permeability, in which the fluid dynamics and relevant conformance control are resolved during secondary and tertiary polymer floodings, once thief zones are apparent. The secondary water flooding did not exhibit an efficient displacement, with fingering and by-passing effects predominantly observed in higher permeability zones and minor oil displacement in the lowest permeability zone. Despite the fingers created by water flooding, polymer flooding showed much higher displacement efficiency throughout all four zones, resulting in significant incremental oil recovery. The secondary polymer flooding also produced more oil than the secondary water flood due to improvement in the mobility control. Lastly, pore-scale mechanisms such as viscous cross-flow between zones was observed during the polymer flood.

Studi Geologi Bawah Permukaan Menggunakan Core Logging Dan Water Pressure Test: Studi Kasus Bendungan Lolak Bolaang Mongondow

North Sulawesi has one large dam located in Pindol Village, Lolak District. The research objective was to determine the lithology of the bedrock of dam foundation, rock class, and subsurface permeability of the dam. The method used in this research is core logging analysis and water pressure test. The bedrock foundations of the dam consist of andesite units, shale units, sandstone units which are included in the Sedimentary Facies Tinombo Formation and Volcanic Tinombo Formation. The formations are included in the Eocene to Early Oligocene Eocene and deposited in the deep marine environment. The foundation rock class is predominantly CM class (rather soft and fairly weathered rock), the rock quality of design is poor-medium characterized by the presence of broken cores and easily crushed in some parts. Lolak Dam has 6 permeability zones, namely very high, high, medium, moderate, low, and very low permeability with an average lugeon value of 4.43 liters/minute. The standard of lugeon value for the dam foundation is Lu3, so it is necessary to repair the drill points on the pilot hole which has a lugeon value of 3 (low, moderate, medium, high, and very high permeability zones) to increase the capacity foundation rock.

Research on Effectiveness and Application of Fixed-Plane Perforation Fracturing Technology in Ultra-Low-Permeability Reservoir

Water flooding development of Chang 6 ultra-low-permeability reservoirs in Ansai lasted for more than 30 years; the front of the water drive has swept the reservoir high permeability zone. As a result, a large amount of residual oil stayed in the reservoir longitudinal low-permeability area. To recover the remaining oil in the low-permeability layers, the fixed-plane perforation fracturing technology is proposed, i.e., using fixed-plane perforation to form a sector stress concentration surface perpendicular to the axis of the wellbore, which makes hydraulic fracture expand radially along the wellbore and control the longitudinal direction of the fracture. Based on the study of residual oil distribution and variation of rock mechanics parameters under long-term injection and production conditions, we simulated and analyzed the effect of fracture initiation under different perforation phases. The optimum perforation phase angle was selected according to the size of the fracture fusion area. According to the fracture simulation under the condition of weak stress difference, the parameters of fracturing operation were optimized with controlling fracture height. A 2-fold increase in ultra-low-permeability reservoir production was achieved by fixed-plane perforation fracturing compared with traditional fracturing technology according to the production data of 78 wells. In this paper, we propose a fixed-plane injection fracturing technique to address the problem of tapping the remaining oil in the longitudinal low-permeability section of the reservoir, which can provide support for tapping the remaining oil in the low-permeability section of the extra-low-permeability reservoir.

Preferential Solute Transport in Low Permeability Zones During Spontaneous Imbibition in Heterogeneous Porous Media

AbstractMultiphase flows in porous media, and the associated solute transport processes, are controlled by a combination of gravity, capillary, and viscous forces. Geologic heterogeneity influences flow and transport processes, yet gaps exist in our understanding of how heterogeneity impacts capillary‐driven transport, such as during spontaneous imbibition. Here we use positron emission tomography, combined with a newly developed method for conducting spontaneous imbibition experiments, to observe solute transport into low permeability regions during imbibition. Using an experimentally parameterized 2D numerical model, we demonstrate how capillary‐driven flow near the imbibition front can carry solutes into low permeability regions. This process displaces solutes from high permeability zones, while the cumulative amount of solute in low permeability zones increases, opposite of what is observed under fully saturated solute transport conditions. These results highlight the complex flow and solute transport behavior that arise during multiphase displacements in heterogeneous geologic porous media.

Experimental study on microscopic mechanisms and displacement efficiency of N2 flooding in deep-buried clastic reservoirs

Current clastic reservoirs with burial depth of more than 5000 m are important energy sources. And microscopic initiation mechanism of residual oil after water flooding has been regarded as the key to improving oil recovery by gas flooding. In this study, an investigation was conducted in the occurrence states and distribution of residual oil of deep-buried reservoirs from microscopic pore scale. We innovatively designed a microscopic visualization experimental equipment for the first time, which broke through the limitations of visualization accuracy, temperature and pressure of the conventional experimental devices. Microscopic visualization experiments of gas injection after waterflooding at 115 °C and 55 MPa were carried out. According to the permeability and pore-throat 0 structure characteristics of deep-buried clastic reservoir, a two-dimensional glass etching micromodel was designed and fabricated. Meanwhile, the occurrence state and formation mechanism of multi-type residual oil were quantitatively characterized by image processing technology. The results showed that there were five kinds of residual oil which were corner, droplet, membranous, columnar and cluster after water flooding. In addition, it was generally concentrated in the fine pore-throats with greater resistance perpendicular to the main stream line. Two mechanisms, immiscible flooding and miscible flooding, were also found in N 2 flooding. Moreover, the injected gas carried, squeezed and dispersed the continuous clusters of residual oil, transforming them into dispersive shapes such as corner and membranous. And a certain amount of microscopic residual oil after water flooding was effectively mobilized by removing the water locking effect. The oil recovery could be improved by 11.49% in low-permeability zone, which was the highest, since the continuous cluster residual oil was decreased significantly. Membranous, columnar and cluster residual oil were well mobilized in the medium-permeability zone, and oil recovery was increased by 8.31%. In comparison, the oil recovery in high-permeability zone was only increased by 2.53%, and there was no cluster oil. Our study highlights the migration characteristic and initiation mechanism of residual oil in porous media under N 2 injection after waterflooding from the perspective of microscopic visualization, which may help to promote the development of deep-buried clastic reservoirs. • Microscopic experimental device was built to simulate 55 MPa and 115 °C. • Micromodels suitable for deep-buried clastic reservoir are designed and made. • A quantitative characterization method of micro-remaining oil occurrence state is established. • The migration characteristics and initiation mechanism during gas injection after waterflooding are clarified.

Identification and research of factors affecting the optimal distribution of well flow rates in space

The paper discusses and research the factors affecting the filtration rate to reduce stagnant zones in the domain and spreading outside the block under consideration. The main hydrodynamic factors in production by In-Situ Leaching are the distribution of permeability in the reservoir and well flow rates. The study of the factors was carried out on the basis of mathematical models using Darcy Law and Law of Conservation of Mass. Calculation was accomplished on a two-dimensional area with an isotropic and non-uniform permeability distribution to determine the effect of permeability on the leached area. The permeability coefficient was distributed respectively over three zones, in the southern part the permeability was low, in the central transition from low to high, respectively, in the northern part there was a highly permeable zone. Three wells were located in the domain, with the production well in the center of the domain. Injection wells are located symmetrically with respect to a horizontal line passing through the center of the area under consideration. The calculation was carried out for three modes of well flow rates with the ratio of the flow rates of the injection wells 0.5 / 0.5, 0.2 / 0.8, 0.8 / 0.2 relative to the flow rate of the production well. On the basis of comparative analyzes of the obtained results, it is concluded that: at the same flow rates, regardless of the permeability of the zones, the results obtained show that the leaching area in the low-permeability zone is larger in comparison with the high-permeability zone; with an increase in permeability, the shape of the leaching zone tends from round to drop-shaped; with an increase in the flow rate of wells in the radius of the leaching zone, it increases if the flow rate of solutions is much higher than the filtration rate.

A Steady Flow of The Viscous Compressible Liquid in Vertical Pipe

In the study of the flow of gas-liquid mixture over circular vertical pipe rising from the deep zone to ground level, it is observed that, the velocity on surface of tube is much more than in the center of flow. Such a picture is seen also in the water filtration process in sands ordering from high permeability zone to lower. Same phenomena occur in transportation of the water carbon nana-tubes. In order to predict behavior of those processes in this paper, we have studied the compressible liquid flow over the circular vertical pipe ordered from the deep zone to the ground surface for some concrete inlet and outlet regimes of the pipe. The Navier-Stokes equations system as a model of study. For certain inlet and outlet regimes of the flow splitting the equation into the cross section and axes variables, the pressure and velocity distribution are found. The Lane-Emden equation arises for determining the pipe cross section velocity distribution, which is also justified by our calculations on the used model.

Fracture permeability estimation utilizing conventional well logs and flow zone indicator

Characteristics of the natural open fractures on the oil and gas reservoirs is crucial in drilling and production planning. Direct methods of fractures studies such as core analysis and image log interpretation are usually not performed in all drilled wells in a field. Therefore, in absence of these data, the indirect methods can play an important role. In this study, an integrated algorithm is introduced to identify the fractures and estimate its permeability employing conventional well logs. First, open fractures were identified and their properties including density, aperture, porosity and permeability were estimated using FMI log. Subsequently, the fracture index log (FR_Index) was estimated utilizing conventional logs including density, micro-resistivity, sonic (compressional, shear and stoneley slownesses), and caliper logs. After that, the fracture index permeability was estimated by improving the FZI permeability equation. The coherence coefficient between two estimated fracture permeability logs is 0.66. A good correlation is observed on the high permeability zones, but the lower correlation on the low permeability zones. It is notified that, in the high fracture permeability zones, the conventional logs are heavily impacted by fracture permeability. However, due to lower vertical resolution of conventional logs compared with the image logs, the conventional logs are less influenced by less dense fracture zones. However, this algorithm can be used with acceptable accuracy in all uncored and image log wells.

Effect of low permeability zone location on remediation of Cr(VI)-contaminated media by electrokinetics combined with a modified-zeolite barrier

Research on electrokinetics-permeable reactive barrier (EK-PRB) remediation to date has mainly focused on homogeneous soils or soils with micro-scale heterogeneities. The potential impact of macro-scale physical heterogeneities, such as stratified layers or lenses, on EK-PRB remediation has not received much attention. This study investigates the effect of a low permeability stratum on EK-PRB remediation of hexavalent chromium (Cr(VI)). Sandbox experiments were conducted to treat Cr(VI)-contaminated kaolinite/sand media, consisting of vertically-layered high permeability (HPZ) and low permeability zones (LPZ), where distance between LPZ and anode (DLA) was 3, 9, or 15 cm. Parameters including current, moisture content (MC), pH, and removal of Cr(VI) were evaluated. With 72 h of EK-PRB treatment, tests with larger DLA (15 cm) had greater Cr(VI) migration from contaminated area to modified-zeolite PRB. Cr(VI), Cr(III), and Cr(Total) removal and energy utilization efficiency followed the trend as: DLA-15 > DLA-9 > DLA-3. MC generally decreased from anode towards cathode and pH was alkaline in all the zones for DLA-3 and DLA-15. In DLA-9 (LPZ in the middle), MC increased and pH was alkaline in HPZs near cathode whereas HPZs near anode were very dry (MC < 1%) and acidic (pH < 5.5). Our results show that the location of LPZ relative to electrode locations has a significant influence on Cr(VI) removal efficiency and macro-scale physical heterogeneity is an important factor to be considered during EK-PRB remediation.

A general physics-based data-driven framework for numerical simulation and history matching of reservoirs

This paper proposed a general physics-based data-driven framework for numerical mod-eling and history matching of reservoirs that achieves a good balance of flow physics and actual field data. Underground reservoir is easily discretized in this framework as a flow network composed of one-dimensional connection elements, each of which is defined by two flow characteristic parameters. Each one-dimensional connection element is divided into some grids, and the cross-sectional area and permeability of the grids on the same connection element are equal. The fully implicit scheme of flow equations and the Newton iteration nonlinear solver concurrently solve all unknown quantities. Then, using actual field data, the simultaneous perturbation stochastic approximation algorithm is used to invert flow characteristic parameters of each connection element, and the unequal constraint that the volume of connection elements should not exceed the total reservoir volume is added to control the data-driven process. To demonstrate the unequal constraint is physical, a test case of a waterflooding reservoir with a high permeability zone is given. A waterflooding reservoir example with five injectors and four producers is used to demonstrate that this framework outperforms earlier techniques, and another case with single-phase depletion development is used to demonstrate that this framework has a high generalization for flow models. In addition, this data-driven framework based on physics is expected to serve as a reference for other fields of science and engineering. Cited as : Rao, X., Xu, Y., Liu, D., Liu, Y., Hu, Y. A general physics-based data-driven framework for numerical simulation and history matching of reservoirs. Advances in Geo-Energy Research, 2021, 5(4): 422-436, doi: 10.46690/ager.2021.04.07

Influence of hydrological communication between basement-rooted faults and hydraulic fractures on induced seismicity: A case study

The mechanical conditions that allow seismogenic faults to be activated in distinctive positions and moments remain uncertain. An integrated approach is proposed to quantify the hydrological connection between stimulated wells and associated seismogenic faults during fracturing stimulation. A case study in Fox Creek, Alberta, was conducted to demonstrate the applicability of this integrated approach. Ant tracking was used to identify the subvertical basement-rooted faults from a three-dimensional seismic reflection survey. A coupled flow–geomechanics simulation was conducted to quantify the well–fault hydraulic connection in terms of pore pressure diffusion and poroelastic stress perturbation during fracturing stimulation. Three identified basement-rooted faults were corroborated by the focal mechanisms and spatial distribution of induced siemsicity events. The negative shear stress gradient indicates the downward shear growth during hydraulic connections. The induced earthquakes were triggered by fluid diffusion through hydraulic fractures along high-permeability fault damage zones downwards into the basement. This basal fault slip was attributed primarily to the elevated pore pressure along the fault plane in response to fracturing fluid injection. The moderate distance (879 m for NS-oriented wells and 749 m for NW-SE-oriented wells) between the future horizontal wellbores and critically-stressed faults could mitigate the effects of well-fault hydraulic connection and reduce the seismicity risks.

Numerical study of fluid injection-induced deformation and seismicity in a mature fault zone with a low-permeability fault core bounded by a densely fractured damage zone

We apply a fully-coupled hydro-mechanical simulation tool to study fluid injection-induced pressure diffusion, poroelastic response, fracture slip, damage growth, and microseismicity occurrence in a complex fault zone. The fault zone has a low-permeability fault core bounded by a high-permeability damage zone, which is characterised by a fracture network with the fracture density exponentially decaying away from the fault core. We employ the discrete fracture network approach to explicitly represent the distribution and behaviour of these fractures in the fault zone. We use the finite element method to solve the coupled governing equations of fluid flow, solid deformation, and damage evolution in the fractured porous rock. We explore a number of scenarios with different orientations for the in-situ stress field and different locations for a constant rate fluid injection. We report an interactive control of fracture density, fracture orientations, in-situ stress state, and injection point position on the seismo-hydro-mechanical behaviour of the fault zone subject to fluid injection. Insight from our research findings may have important implications for injection-related geoengineering activities such as the development of enhanced geothermal systems and unconventional hydrocarbon reservoirs.