Fractured Carbonate Research Articles

Controls of dolomitization and bed thickness on fracture networks in Lower Carboniferous carbonates in southern Belgium

Fracture networks in limestone and dolostone quarries in southern Belgium were analyzed as analogues to fractured subsurface Lower Carboniferous carbonates in the Campine-Brabant Basin (northern Belgium, southern Netherlands and westernmost Germany), which are considered as potential geothermal reservoirs. This study focuses on the difference in fracture density, intensity and connectivity in dolostone and limestone quarry walls, as well as on the relationship between bed thickness and fracture density/intensity. Bedding planes and fractures were interpreted based on orthorectified images of quarry walls. Statistical tests show that fracture density and intensity are significantly larger in the dolostones than in the limestones, which is explained by rock mechanical properties. Fracture connectivity is also highest in the studied dolostones. Interpreted bed thickness is significantly larger in limestones than dolostones, but no correlation is present between bed thickness and fracture density or intensity. This may be explained by the low percentage of bed-bounded fractures in the quarry walls. Fracture density, intensity and connectivity are key parameters influencing permeability, especially in carbonates with low matrix porosity. The results suggest that, in light of fracture properties, Lower Carboniferous dolostones might possess better geothermal reservoir characteristics than limestones.

3D Modeling of Fracture-Cave Reservoir from a Strike-Slip Fault-Controlled Carbonate Oilfield in Northwestern China

A giant strike-slip fault-controlled Fuman Oilfield has been found in the Ordovician fractured carbonates of the Tarim Basin. However, conventional seismic methods are hardly able to distinguish the fractured reservoir and its connectivity in the ultra-depth (>7000 m) carbonate fault zones. We propose thin-likelihood and tensor-thickness process methods to describe the fracture network and large cave reservoir, respectively. Together with the two methods for 3D visualization of fracture-cave reservoirs, we had an application in the ultra-deep well deployment in Fuman Oilfield. The results show that the fracture network and cave reservoir can be 3D-imaged more clearly than conventional methods. The fracture network and cave reservoir show distinct segmentation by the fault assemblage in Fuman Oilfield. Furthermore, 3D modeling is favorable for the reservoir connectivity description along the carbonate fault zones. There are three distinct reservoir models: fault core-, fault damage zone- and overlap zone-controlling fractured reservoirs along the fault zones. This revealed variable fractured reservoirs that are related to fault maturity and segmentation. The method has been widely used in fracture-cave reservoir description and subsequent well optimization, suggesting a favorable method for economic oil exploitation in the ultra-depth reservoirs. This case study is not only useful for the complicated reservoir 3D description and modeling but also helpful for well employment to provide support for the target evaluation and optimization in ultra-depth fractured reservoirs.

Iterative sequential robust optimization of quantity and location of wells in field development under subsurface, operational and economic uncertainty

Determination of optimal quantity and location of wells is a crucial step in any field development project. Multiple challenges exist in the real-world projects, such as gigantic multidimensional search space and complex parameterization of the problem. To address these challenges, we present an iterative sequential optimization framework that consists of multiple stages for optimizing number and location of producers and injectors. Once the initial guesses have been established, the first optimization stage begins in order to determine the optimal number of producers and injectors. Next, a two-stage process is used to determine the best location for each well. By optimizing the number and location of wells, well type is optimized implicitly and does not need to be included in the optimization process as an individual decision variable. To consider the dependency and coupling between parameters, the entire optimization process is repeated iteratively up to a stopping point. The proposed approach is highly flexible and can be extended to include other potential decision variables of field development projects. We test the proposed methodology on UNISIM–II–D, a realistic benchmark case that represents pre-salt reservoirs in deep offshore Brazil, which are light-oil fractured carbonates with large volumes of CO2-rich associated gas. In our application, all producers and injectors are equipped with internal control valves (ICVs), all produced gas is reinjected into the reservoir, and water-alternating-gas with CO2 (WAG-CO2) is used to increase oil recovery and ensure that the produced CO2, as a harmful greenhouse gas, can be safely discarded underground. We use the iterative discrete Latin hypercube (IDLHC) optimization algorithm. To achieve a robust decision, we consider subsurface, operational and economic uncertainties by considering nine representative reservoir models and three economic scenarios. Based on the results, the proposed framework can provide an appropriate solution containing optimal quantity of wells, their locations and types in realistic cases with large search spaces and complex parameterizations.

AVO study on a known geothermal reservoir located in the fractured carbonate formations of the pre-Cenozoic basement, Northwest Hungary

Amplitude Versus Offset (AVO) analysis has been successfully applied in the hydrocarbon industry for more than three decades. This effective tool of the joint seismic and well-log data processing enables to predict and analyze fluid saturated porous geological formations. AVO methodology is based on the anomalous behavior of the pre-stack reflected amplitudes observed from fluid bearing rocks. However, the potential of AVO methodology is still unexploited in geothermal exploration, although the lithology and rock physical properties are very similar. In this study, we summarize the theoretical backgrounds and calculate synthetic AVO responses of a known geothermal reservoir located in the fractured carbonates of the Mesozoic basement. We demonstrate that the AVO response of a deep geothermal reservoir can be quite different from the amplitude response observed from a hydrocarbon bearing clastic formation. AVO attributes of the investigated geothermal reservoir are presented, and the potential of its detection by seismic amplitude data are discussed.

Fractures in the Niagara Escarpment in Ontario, Canada: distribution, connectivity, and geohazard implications

AbstractThe Niagara Escarpment is a geological feature located in southern Ontario, Canada, and the northeastern United States, comprising highly fractured sandstone, shale and carbonates deposited during the Ordovician and Silurian periods. Differential erosion of the strata has generated a steep cliff face which bisects the city of Hamilton, Ontario. Geological fractures are widespread in the escarpment and result in the formation of unstable blocks of rock subject to erosion through rockfall. This presents structural stability issues of concern due to the proximity of the escarpment to urban infrastructure. We quantify and analyse fracture networks in the escarpment using a combined field- and numerical-modelling-based approach. The location, orientation and aperture of fractures were documented from local outcrops using scanline and area survey methods. Clusters of poles describing the orientation of geological discontinuities were identified in spherical projections, defining three sets: (1) a sub-vertical stratabound set striking N–S, (2) a sub-vertical stratabound set striking E–W, and (3) a set parallel to horizontal sedimentary bedding planes which we infer controlled sub-vertical fracture geometry. Discrete fracture network modelling of fracture sets highlights their high degree of connectivity, and contribution to local geohazards, and quantifies their role in controlling fluid flow through escarpment strata, which is dependent on fracture aperture. Additionally, bedding planes have the potential to act as free surfaces, facilitating stress conditions in which approximately cuboid blocks are produced, and increasing the risk of rockfalls. We conclude that fractures present a first-order control on the fluid-flow properties and stability of the Niagara Escarpment.

Capacitive eye tracker made of fractured carbon nanotube-paper composites for wearable applications

The uniqueness of eyes, facial geometry, and gaze direction makes eye tracking a very challenging technological pursuit. Although camera-based eye-tracking systems are popular, the obtrusiveness of their bulky equipment along with their high computational cost and power consumption is considered problematic for wearable applications. Noncontact gaze monitoring using capacitive sensing technique has been attempted but failed due to low sensitivity and parasitic capacitance. Here, we study the interaction between a novel capacitive sensor and eye movement for wearable eye-tracking. The capacitive sensors are made of a pair of asymmetric electrodes; one comprising carbon nanotube-paper composite fibers (CPC) and the other being a rectangular metal electrode. The interaction between the asymmetric sensor and a spherical object mimicking an eyeball is analyzed numerically. Using a face simulator, both single- and differential capacitive measurements are characterized with respect to proximity, geometry, and human body charge. Using a prototype eye tracker, multiple sensor locations are studied to determine the optimal configurations. The capacitive responses to vertical and horizontal gaze directions are analyzed in comparison to those of a commercial eye tracking system. The performance is demonstrated for sensitive eye-movement tracking, closed-eye monitoring, and human-machine interface. This research has important implications for the development of capacitive, wearable eye trackers, which can facilitate fields of human-machine interface, cognitive monitoring, neuroscience research, and rehabilitation.

Productivity prediction with consideration of stress-sensitive permeability in naturally fractured carbonate reservoir

The aim of this paper is to illustrate the impact of stress-sensitive permeability on productivity in naturally fracture carbonate reservoirs. First, stress sensitivity evaluation experiments were conducted on artificial cores with matrix, uncemented fracture, partially- cemented fracture and fully-cemented fracture by measuring their permeability in the process of increasing confining pressure. Then, a new mathematical model for productivity prediction in naturally fractured carbonate reservoir with consideration of stress-sensitive permeability is developed. Comparisons have been made between the new model prediction results and field measured data to verify the accuracy of the new model. Finally, based on the validated model, the detailed impact of permeability modulus on productivity is analysed. The experiment results show that the strength of stress sensitivity, evaluated by permeability modulus, of cores with uncemented fracture and partially-cemented fracture is generally an order of magnitude larger than that of cores with matrix and fully-cemented fracture. The results show the new model can be simplified to the classic model (Vogel equation) under the condition of the stress sensitivity being not taken into account, which means the class model is corresponding to a special case of this new model. Field application shows that the new model is reliable and correct. Moreover, with the help of the new model, it is found that the impact of stress-sensitive permeability on productivity increases with increasing permeability modulus and decreasing flow bottom hole pressure.

Parameter Effect Analysis of Non-Darcy Flow and a Method for Choosing a Fluid Flow Equation in Fractured Karstic Carbonate Reservoirs

Fractured karstic carbonate reservoirs have obvious multi-scale characteristics and severe heterogeneity due to the development of abundant karst caves and fractures with different scales. Darcy and non-Darcy flows coexist due to this property. Therefore, selecting the appropriate flow equations for different regions in the numerical simulation of fluid flows, particularly two-phase and multiphase flows, is a critical topic. This paper compares and analyses the displacement distance differences of waterfront travel using the Darcy, Forchheimer and Barree–Conway equations, as well as analyzes the influence of the Forchheimer constant, fluid viscosity, flow rate and absolute permeability on inertia action based on the Buckley–Leverett theory. The results show that the Forchheimer number/Reynolds number of water/oil two-phase flow is not a constant value and varies with water saturation, making it difficult to determine whether the inertial action should be considered solely based on these values; the influence of inertial action can be measured well by comparing the difference between the displacement distances of the waterflood front, and the quantitative standard is given for the selection of the flow equation of different regions by calculating the allowable error of the displacement distance of the waterflood front. The magnitude of the inertial effect is affected by the physical properties of the fluid and reservoir medium and the fluid velocity. The smaller the difference in the viscosity of the oil/water fluid, the smaller the inertial effect is. This technique was used a preliminary attempt to analyze the fractured karstic carbonate reservoirs at Tarim, and the results confirmed the validity of the method described in this article.

A new numerical simulation method of hydrogen and carbon compounds in shale reservoir

Hydrogen energy can be produced by the decomposition of hydrogen and carbon compounds. A numerical analysis method of accuracy and efficiency provides important reference value for optimizing development plans and predicting production performance of hydrogen and carbon compounds. In this work, embedded discrete fracture model (EDFM) is used to study the production performance of hydrogen and carbon compounds under non-liner seepage under the threshold pressure gradient and complex fracture systems consist of the hydraulic fractures, secondary fractures, natural fractures. A dual-permeability model of the same case is also constructed as a comparison study to analyze the development of hydrogen and carbon compounds. On this basis, the influence of threshold pressure gradient on production of hydrogen and carbon compounds is quantitatively evaluated in this paper to modify the numerical model and a novel method for the simulation of fractured hydrogen and carbon compounds reservoirs is provided. Through model comparison, the impact of fractures in the reservoir on production can reach 289.1%. A dual-permeability model of the same case is also constructed as a comparison study to analyze the development of the reservoir and the result shows a 7.9% distinction on the cumulative production. It is analyzed that when the threshold pressure gradient is increased from 0.1 MPa/m to 0.6 MPa/m, the output decline of different models ranges from 6% to 15% and a novel method improving model fidelity for the simulation of fracture reservoirs is provided.

Mini Review on Stability and Formation of Emulsion During Injection of Smart Water in Fractured Carbonate Reservoirs

One of the most commonly used methods of enhanced oil recovery for use in carbonate reservoirs is the smart water injection method. Asphalt nitic compounds in the oil serve as natural surfactants and form water emulations in the oil when they are placed at the water and oil contact points. Besides, the salt contained in saltwater also contributes to the emulsion stability. Given that low-salty water and seawater are used for enhanced oil recovery, this process also increases the likelihood of the formation of W/O emulsions, so the assessment of the formation of W/O emulsions with low-salty water and seawater compounds and the stability of these emulsions due to the presence of different ions, can bring the conditions of formation of natural emulsions closer to actual events. Distinctive properties of injected water in order to form microemulsions of W/O and, the effect of concentration of ions in the injected smart water on the oil extraction efficiency have been investigated. Also, the formation of water emulsion in oil and its stability in oil sweeping in the formation in the case of smart water injection and its effect on the oil extraction efficiency have been discussed in full detail by presenting experimental results.

Research on well selection method for high-pressure water injection in fractured-vuggy carbonate reservoirs in Tahe oilfield

Carbonate fractured vuggy reservoir in Tahe oilfield belongs to fractured vuggy reservoir with strong heterogeneity. After a period of production, the elastic energy of the cave formation weakens caused insufficient liquid supply, It is faced with a series of problems in some single wells, such as low water injection efficiency, high water cut, short production period, and so on. The introduction of high-pressure water injection technology can greatly restore the productivity of single wells and improve reservoir recovery. It is one of the effective new technology to develop fractured vuggy carbonate reservoirs. At present, this technology is still in the initial stage, with no clear guide method that selecting wells for high-pressure water injection. Among them, the determination of the high-pressure water injection well selection method is particularly important for the development effect of a single well. Based on the analysis of the mechanism of high-pressure water injection and combined with the field data, this paper formulates the well selection method of high-pressure water injection from three aspects: Karst Characteristics, reservoir structure and reservoir parameters:①Karst geological data show the characteristics of oil-increasing substances such as many abnormal bodies around the well and wide lateral distribution; ②The reservoir structure has multiple sets of connected karst caves with connectivity potential; ③After the failure of conventional water injection, the fracture passage effect is poor and the energy of the remote well is insufficient. The independent high-pressure water injection development method can reduce the channel seepage resistance, expand the scope of the injected water, and realize increased production. Up to now, Tahe oilfield has used the method to implement high-pressure water injection 41 well, achieving an average single well cumulative incremental oil production of 3211 tons, with an effective rate of 85.4%, which has a satisfactory application value.

A Study of the Thin Film-Coated Swelling Retarding Particles in Fractured Carbonate Reservoirs for Water Plugging and Profile Control

T oilfield is the fractured-vuggy carbonate reservoir at a temperature of around 130 °C, with salinity of up to 22 × 104 mg/L. In order to solve the problem of the high water cut in the late development stage of T oilfield, we selected XN-T from 27 kinds of swelling retarding particles by testing their swelling capacity, and coated a thin film to improve its retarding swelling capacity. The mechanisms of strong water absorption and water-holding abilities of particles were analyzed by infrared spectrometry and SEM. In the core flow experiment, the plugging rate was found to be 98.42%. Finally, the injection parameters of the coated particles were optimized to maximize the water plugging and profile control ability, resulting in an optimal particle size of 0.4–0.6 mm and a mass fraction of 10%.

A novel method for determining the binomial deliverability equation of fractured caved carbonate reservoirs

The binomial deliverability equation is one of the essential parameters that control the fluid production/injection rate from wells. The presence of caves and fractures introduces many difficulties related to the determination of the binomial deliverability equation of fractured caved carbonate reservoirs. In this work, a novel method for determining the binomial deliverability equation of fractured caved carbonate reservoirs is proposed for the first time. First, the detailed procedure of our method is illustrated. More specifically, the superposition principle is used to derive the expressions of (Δ p / Q ). The pressure buildup data and type curve matching are employed to induce the dimensionless bottom-hole pressure solution. Sequentially, the binomial deliverability equation can be obtained through the least square method. Then, we employ our method to a simple case and compare the calculation results with the literature data to calibrate the accuracy of our method. Next, we present the applications of our method to two example wells from the Shunbei Oilfield, western China. The results show that our method is reliable. Moreover, the results also indicate that our method is more suitable for fractured caved carbonate reservoirs than the deliverability test. Meanwhile, through the calculations of massive field data and theoretical analysis, we conclude three constraints on the input parameters. They are as follows: (i) the flow rate of each production system must be incremental; (ii) the production time must satisfy t p 1 = t p 2 – t p 1 = t p 3 – t p 2 = t p 4 – t p 3 ; and (iii) the flow rate must satisfy Q 2 = 2 Q 1 , Q 3 = 3 Q 1 , Q 4 = 4 Q 1 . Finally, we prove the necessity of these constraints. • A new method for determining the binomial deliverability equation of fractured caved carbonate reservoirs is proposed. • Applications of proposed method on two field wells are presented. • Three constraints on input parameters are concluded and their necessities are calibrated.

Fundamental constraints of lithologically-controlled fault networks on gas migration and accumulation for fractured carbonates in the western Sichuan Basin, China

The structure of subsurface fault networks, which has a significant effect on hydrocarbon migration, is inherently difficult to recognize and map. 3D seismic surveys provide an opportunity to map the fault system within a carbonate reservoir of Xinchang in the western Sichuan Basin, China. We calculated attributes from the seismic reflection data that covers an area of 1330 km2, including variance, edge detection, dip-magnitude and dip azimuth. We focused on the Triassic Leikoupo Formation of dolostone, at ∼6 km depth, adjacent to the Longmen Shan thrusting range. The mapped attributes display (1) a primary network of faults in an orthogonal pattern in the anticline, striking East-West and North-South, and (2) a secondary, conjugate fault set in the fold limb, striking Northeast and Northwest with a length range of 1–10 km. The latter set of conjugate faults are confined to a 300 m-thick layer of dolostone, diminishing into underlaying unit of anhydrite. We envision that the conjugate fault networks and associated fractures enhance gas charging and reflect a model of self-sourced migration and accumulation in the Leikoupo Formation. These results are significant for sweet-spot evaluation of carbonate reservoirs in the Sichuan Basin, and provide insights for understanding the migration of subsurface fluids.

Azimuthal P–P prestack seismic prediction of fractures for superdeep carbonate reservoirs in northwest China

Ordovician fractured carbonates under study are over 7000 m deep in northwest China. Multistage tectonic activities result in numerous fractures along the strike-slip faults, accompanied with karst collapses due to atmospheric freshwater seepage. The resultant cave-fracture system provides numerous channels favorable for the migration and storage of hydrocarbons. Azimuthal anisotropy analyses with wide-azimuth and high-density 3D seismic data facilitate fracture estimation from migrated CRP gathers in this area. Compared with azimuthal velocity variations, azimuthal amplitude variations are quite sensitive to fractures, but suffer many negative factors. Major difficulties with azimuthal amplitudes to map superdeep fractured reservoirs include non-uniform distribution of azimuths and offsets, extremely low S/N ratio (SNR), anisotropic effect of strike-slip faults, and shielding effect of overlying irregular igneous strata. We propose an integrated scheme with azimuthal P–P amplitude/frequency attributes for prestack prediction of fractures based on the migrated CRP gathers. First, we analyze the distribution of azimuths, offsets, and bins to identify appropriate bins with the best range of offsets and the uniform distribution of azimuths. The selected wide-azimuthal CMP gathers are regrouped in terms of five azimuths, followed by azimuthal prestack migration. The resulting subazimuthal CRP gathers are optimized by denoising, flattening by residual static correction, and wavelet shaping to improve both SNR and resolution. We then conduct a local stacking in 100 m × 100 m bin for the best range of offsets from 1000 to 5600 m, followed by matched filtering to remove the footprint effect of overlying igneous strata. Frequency-related amplitude attributes are extracted for sensitive analyses in azimuths by ellipse fitting, yielding several optimal attributes for fracture prediction. We demonstrate that the coupled amplitude and frequency attributes in terms of energy percentages are the best in this area. Case studies show the applicability of the presented scheme for detecting superdeep fracture sets from extremely low SNR seismic data.

Improving drilling speed and borehole quality in ultra-deep complex formations through rock mechanics research

Halahatang oilfield in Tarim Basin is a typical ultra deep fractured vuggy carbonate reservoir, which is the main production area of crude oil in Tarim Basin. The wellbore instability is serious in Triassic and lower strata (the borehole enlargement rate is 22% - 31%). Due to the complex rock characteristics, the drilling cycle for single well is long (124 days on average), and it is difficult to speed up. Based on the log interpretation curves, the calculation methods of pore pressure, collapse pressure and fracture pressure profiles established, and the spatial distribution characteristics of three pressures in this area were analysed; The rock drillability, rock hardness, compressive strength and abrasiveness of the roller bit and PDC bit single well measured by laboratory tests. Based on the statistical regression method, the relationship between the above drilling rock mechanical parameters and logging acoustic time difference and the formation drillability profile single were studied. The research results guide the drilling design optimization and operation of 15 wells in Ha 8 and Ha 12 blocks, The average drilling cycle is reduced by 21% (from 124 days to 98 days), and the hole enlargement rate is reduced from 24% to less than 10%.

Reflection coefficients of P‐waves in partially saturated fractured media

ABSTRACTWave‐induced fluid flow, an important mechanism in seismic wave attenuation, is considered in the amplitude variation with the offset technique. In a fractured marine carbonate reservoir, fractures and pores develop simultaneously, such that wave‐induced flow is an important mechanism in attenuation caused by the fluid flow between pores as well as between pores and fractures. However, these two types of attenuation are typically investigated separately or studies assume that the pores and fractures are dry or saturated by the same fluid. Rock pores are usually saturated by a mixture of two or more fluids, such that the fracture and pore filling fluids may be different. During variation with offset reservoir prediction and fluid identification, the influence that the porosity, fracture, and fluid have on the P‐wave reflection coefficient should be considered. The patchy saturation model can describe the seismic wave dissipation caused by the wave‐induced flow between pore fluids, whereas the Norris model can describe seismic wave dissipation caused by the fluid flow between fractures and pores. This study considers both the patchy saturation model and Norris model to calculate the amplitude variation with the offset P‐wave reflection coefficient under different conditions. Combining the saturation and Norris models forms a new model, which is regarded as a transversely isotropic medium with a vertical symmetric axis, and can be extended to any incident angle through the relaxation function and the high‐ and low‐frequency elastic limits of the stiffness tensor, where the complete effective stiffness tensor of the new model can be obtained. Finally, the amplitude variation with offset reservoir technology is used to determine the influence of model parameters on the reflection coefficient of P‐waves under different angles and frequencies, including fracture weakness, fluid saturation and pore fluid saturation.

High-resolution electrical resistivity tomography and seismic refraction for groundwater exploration in fracture hard rocks: A case study in Kanthan, Perak, Malaysia

• High-resolution ERT and seismic results were validated by tube-well drillings. • Sharp vertical boundary between high and low resistivity zones indicates fault zone. • Depression zone in seismic refraction depth profile indicates highly fractured rock. • DLS method of Wenner-Schlumberger + dipole–dipole arrays are the most effective. • Groundwater source is discovered at the intersection of major discontinuities . This research article describes the integration of high-resolution electrical resistivity tomography (ERT) and seismic refraction to explore potential groundwater in fracture carbonate hard rocks. Data Levels Synthesization (DLS) method is developed where the data levels of two different optimized arrays were merged to produce one final subsurface resistivity image to achieve high-resolution ERT. Numerical modeling was initially conducted on three different geoelectrical arrays. The results of before and after applied DLS method were compared to evaluate the effectiveness of each geoelectrical array to delineate fracture and anomalies accurately. Lineament map is constructed beforehand to map the major discontinuities which could possibly be the potential target for water-containing and water-conducting zones in the subsurface. Two geophysical survey lines were conducted where each survey line covered both ERT and seismic refraction methods. Two tube wells were successfully drilled exactly on the fracture zone with a flow rate around 1000 L/h. The potential water-containing zones within the subsurface limestone bedrock were identified as zones of low to moderate geoelectrical resistivity values ranging from 10 to 400 Ωm and V p velocities exceeding 2000 ms −1 . The fault zones were determined by sharp vertical boundary between the high and low resistivities zones in ERT image and lateral decrease in the V p velocities of the limestone bedrock and depressions along the overburden-bedrock interface. The DLS method of Wenner-Schlumberger and dipole–dipole arrays had been proven effective in enhancing the horizontal and vertical resolutions to produce high-resolution ERT image validated with seismic refraction, lineament map, and tube well drillings.

Study on Water Injection Indicator Curve Model in Fractured Vuggy Carbonate Reservoir

Fractures and cavities are very well developed in fractured vuggy carbonate reservoirs in Tahe Oilfield, showing obvious constant volume or approximate constant volume characteristics, and the development of karst vuggy reservoirs is characterized by strong randomness, locality, heterogeneity, and discontinuous development, which has a great impact on oilfield development effect. The application of conventional reservoir engineering methods in this kind of reservoir has many limitations. The traditional water injection indication curve is mainly based on a sandstone reservoir, ignoring the elastic energy of the water body in a reservoir and the combination relationship of fracture and cavity, which can not meet the needs of the carbonate reservoir. According to the principle of volume balance of constant volume body and considering the elastic energy of original formation water, a new model of improved water injection indication curve and the original water-oil ratio of carbonate reservoir is proposed, and the chart of water injection indication curve is established. Compared with other methods, this method has the advantages of low cost and accurate identification results. The calculated reservoir parameters such as single well-controlled reserves, well-controlled water volume, and original water-oil ratio have high reliability, and the chart is easy to use. The model is applied to the Yuejin block of Tahe Oilfield, and the results show that the improved model is consistent with the results of other test methods, such as high-precision seismic combined with fracture cavity carving technology, which indicates that the model has strong reliability.

Mechanical investigation of rock-proppant interaction with focus on geothermal applications

Since decades proppants have been used to enhance hydraulic pathways for the exploitation of hydrocarbon reservoirs. These technologies may also be adapted for geothermal applications, but geothermal reservoirs rocks strongly differ from those typically targeted by hydrocarbon industries. Therefore, the mechanical interaction between conventional proppants and geothermal reservoir rocks and their effect on hydraulic properties need to be investigated in more detail to maximize the success of such method adaption. In principle, two mechanical requirements must be fulfilled: (1) proppants must withstand the stresses that are present in a reservoir, and (2) proppants must not penetrate the rock formation of the reservoir, because this would reduce the fracture conductivity. Fine mobilized rock- or proppant particles can also clog the fracture. For the mechanical suitability of proppants, uniaxial compressive strength tests and long-term creep tests were carried out in the laboratory. The test setup consists of a proppant monolayer placed between two cylindrical rock samples that were axially loaded. We determined Young’s moduli and creep rates for sample stacks with various proppants under different stress conditions. The laboratory tests are part of the ZoKrateS Project, which aims at showing the feasibility of enhancing fractured carbonate rock mass by proppant placement for geothermal applications.