Typical Sandstone Research Articles

Study of fracture processes in sandstone subjected to four-point bending by means of 4D X-ray computed micro-tomography

<p class="Abstract">High-resolution X-ray computed micro-tomography (CT) is a powerful technique for studying the processes of crack propagation in non-homogenous quasi-brittle materials such as rocks. To obtain all the significant information about the deformation behaviour and fracture characteristics of the studied rocks, the use of a highly specialised loading device suitable for the integration into existing tomographic setups is crucial. Since no adequate commercial solution is currently available, a completely newly-designed loading device with a four-point bending setup and vertically-oriented scanned samples was used. This design of the loading procedure, coupled with the high stiffness of the loading frame, allows the loading process to be interrupted at any time and for CT scanning to be performed without the risk of the sudden destruction of the scanned sample.</p>This article deals with the use of the 4D CT for the visualisation of crack initiation and propagation in clastic sedimentary rocks. Two types of quartz-rich sandstones of Czech provenance were used for tomographic observations during the four-point bending loading performed on chevron notched test specimens. It was found that the crack begins to propagate from the moment that ca. 80 % of the maximum loading force is applied.

Geological, fluid inclusion microthermometry and geochemical constraints on the ankeritic-sideritic iron deposits in the Delijan mining district, Malayer-Esfahan metallogenic belt, Iran

The Kahak, Raveh, and Khoreh stratabound sideritic-ankeritic iron deposits are located in the Malayer-Esfahan metallogenic belt (MEMB), Iran. Geological, geochemical, fluid inclusion and S isotope studies have been carried out on the Kahak, Raveh, and Khoreh deposits which are hosted by different types of Lower Cretaceous dolomite, sandstone, and tuff in the Delijan mining district (DMD). Ankerite and siderite ores display a strong lithological control and form stratabound stacked ore lenses hosted in different horizons by Kc2, Kcv, Kc3, and Km units. Economic orebodies are restricted to the hanging wall of the syn-sedimentary normal faults. Three ore types can be distinguished based on the petrographic studies: stringer zone ore facies, bedded ore facies, and massive-replacement ore facies. Ore minerals are predominantly ankerite, siderite, barite, chalcopyrite, sphalerite, galena, and pyrite. Ore mineralization in the Kahak, Raveh, and Khoreh deposits has emplaced in two stages. The fine-grained ore bands (stage 1) which are intricately interlayered with host rock beds, exhibit sedimentary textures such as lamina and bedding and indicate a syn-sedimentary origin. The coarser-grained stage 2 ores show massive and vein-veinlet textures that are considered to form by replacement during sub-seafloor fluid flow. Hydrothermal alteration minerals developed in the wall rock include dolomite, quartz, and calcite. A microthermometric study of fluid inclusions from the barite samples indicates homogenization temperatures between 162 and 210 °C. Salinities of ore-forming fluids range from 7.8 to 16.8 wt% NaCl eq. Fluid inclusion studies suggest that the ore-forming fluids were derived from basinal or formational brines. Fluid mixing (basinal brine and seawater) may have played an important role during Fe mineralization. Calculated δ34S values for the ore fluid vary between + 10.69 and + 31.98‰. Sulfur isotopic compositions suggest that the source of sulfur for barite was derived from seawater. These data show that the Kahak, Raveh, and Khoreh ankeritic-sideritic iron deposits are comparable with those of sub-seafloor carbonate-replacement SEDEX-type deposits.

Study on Crack Classification Criterion and Failure Evaluation Index of Red Sandstone Based on Acoustic Emission Parameter Analysis

The acoustic emission (AE) characteristics of rock during loading can reflect the law of crack propagation and evolution in the rock. In order to study the fracture mode in the process of rock fracture, the AE characteristics and crack types of red sandstone during fracture were investigated by conducting Brazilian indirect tensile tests (BITT), direct shear tests (DST), and uniaxial compression tests (UCT). The evolution law of AE event rate, RA and AF values, and the distribution law of RA–AF data of red sandstone samples in three test types were analyzed. Based on the kernel density estimation (KDE) function and the coupling AE parameters (RA–AF values) in DST and BITT, the relatively objective dividing line for classifying tensile and shear cracks was discussed, and the dividing line was applied to the analysis of fracture source evolution and the failure precursor of red sandstone. The results show that the dividing line for classifying tensile and shear cracks of red sandstone is AF = 93RA + 75. Under uniaxial compression loading, the fracture source of red sandstone is primarily shear source in the initial phase of loading and tensile source in the critical failure phase, and the number is far greater than shear source. K = AF/(93RA + 75) can be defined as the AE parameter index, and its coefficient of variation CV (k) can be used as the failure judgment index of red sandstone. When CV (k) < 1, it can be considered that red sandstone enters the instability failure phase.

Influencing Factor Analysis on the Fractured Tight Sandstone Gas Reservoir Characteristics: A Case Study of Bozi 3 Gas Reservoir in the Tarim Basin

The Bozi 3 gas reservoir in the Tarim Basin is a typical ultra-deep fractured tight sandstone gas reservoir, in which the main formations are the Cretaceous Bashijiqike Formation and the Baxigai Formation. The reservoir has the characteristics of deep burial, tight reservoir matrix, well-developed fractures, large differences in well productivity, and regional pressure distribution. These characteristics bring development challenges in well deployment, production allocation, gas production rate optimization, and production improvement. The main reservoir of Bozi 3 is deposited in the braided river delta, fan delta, and shallow lake environment with adequate provenance and a strong hydrodynamic environment, which provides favorable depositional conditions for the formation of thick sandbodies. Although the buried depth of the Bozi 3 gas reservoir is over 6,000 m, it has undergone an evolutionary process of long-term shallow burial in the early stage and rapid deep burial in the late stage, which protects the primary pore, and the finally formed reservoir has the characteristics of an extra-low pore and ultra-low permeability pore structure. Late tectonic movements caused the Bozi 3 gas reservoir to experience strong uplift under a strong nappe-thrust environment, forming a large number of high-angle fractures around the faults. Although the fracture distribution is inhomogeneous, tensile fractures at the top anticline have a low-filling degree and good effectiveness, which effectively improve Bozi 3 reservoir properties. Through analysis of the reservoir characteristics and influencing factors of the Bozi 3 gas reservoir, it is concluded that the difference in reservoir characteristics is the main reason for the large difference in production of adjacent wells and zonal distribution of formation pressure at the early development. This study can also provide a reliable geological basis for well deployment, production allocation rationalization, and gas production rate optimization in the study area.

Salt Accumulation in Heritage Sandstones Under Continuous Wick Effect Conditions

ABSTRACT During the weathering of stone monuments, salt accumulation and crystallization lead to salt damage. In this study, we investigated the evolution of heritage sandstone salt accumulation, considering the porous system of the stone and humidity conditions. Two types of heritage sandstone were collected from the North Grotto Temple (NGT sandstone, coarse sandstone) and the Leshan Giant Buddha (LGB sandstone, fine sandstone) to conduct a salt weathering test simulating the continuous wick effect under different relative humidity conditions. We monitored the sandstone evaporation rate and macroscopic surface phenomena during the simulation test. We analyzed the sandstone after 10, 20, 40, 80, and 160 days of salt solution rise (capillary action) to investigate the salt accumulation within different stone sections and on the stone surface. Additionally, ultrasonic wave velocity tests were conducted to determine salt damage within the sandstones. Results showed that salt accumulation increased over time in both sandstone types and increased along the direction of capillary rising height, but showing different increasing gradients (i.e. with increasing height, salt accumulation increased only slightly in the NGT sandstone but rapidly in the LGB sandstone). Notably, different salt distributions in sandstones further affected the development of salt damage and variations in the evaporation rate. This study aims to comprehensively understand weathering and salt accumulation in monumental rocks, providing valuable suggestions to effectively preserve these monuments.

Estimation of Brittleness Indexes from Petrographic Characteristics of Different Sandstone Types (Cenozoic and Mesozoic Sandstones), Markazi Province, Iran

Estimation of Brittleness Indexes from Petrographic Characteristics of Different Sandstone Types (Cenozoic and Mesozoic Sandstones), Markazi Province, Iran

Influence of physicochemical variables on polymer adsorption in porous media

HPAM type polymers and modifications with ATBS (Acrylamide Tertiary Butyl Sulfonated) units are used for EOR processes. Polymer adsorption is key to the success of these processes and is affected by variables such as molecular weight, hydrolysis, salinity, and permeability of the porous medium. Nevertheless, few studies corelate the dependence of these variables with adsorption. This work presents experimental results of the influence of variables on the dynamic adsorption of different polymers using sandstone type porous media. Modified polymers show adsorption less than 10 μg/g in low permeability and Sor condition. The adsorption of modified HPAM and HPAM polymers has an inverse relationship with molecular weight and permeability. At higher molecular weight, fewer pores are accessed due to their hydrodynamic radius and lower permeability, greater mechanical and hydrodynamic retention. Water salinity and hardness are directly related to adsorption, with less influence for modified HPAM.

Study on Sedimentary Facies and Reservoir Characteristics of Paleogene Sandstone in Yingmaili Block, Tarim Basin

Block Yingmai 7 is structurally located in the western segment of the southern margin of the Kuqa Depression in the Tarim Basin. In the foreland basin, huge continental Mesozoic and Cenozoic strata have been deposited. In recent years, the Paleogene bottom sandstone section has been the main oil and gas exploration horizon. In order to further improve the oil and gas exploration effect of the Paleogene bottom sandstone in the study area and improve the accuracy of reservoir prediction, based on the related theory of sedimentology and petrology, this paper analyzes and studies the cores obtained by drilling in the Paleogene through laboratory core analysis experiments. The study shows that the Paleogene bottom sandstone is a braided river delta sedimentary system, and the sedimentary microfacies are mainly underwater distributary channels. The sandstone type is mainly light gray lithic feldspar fine sandstone, the sandstone debris particle sorting degree is medium-good, and the roundness is sub-edge-sub-circular. The microscopic characteristics of the reservoir are large pore throat radius, low displacement pressure, mainly intergranular pores, and good pore connectivity. It is a thin-layered mesoporous, medium-permeable, large-throat, and strongly heterogeneous reservoir. Finally, a classification evaluation table of reservoirs in block Yingmai 7 is established, and it is considered that the reservoirs of types I and II are enriched areas of oil and gas resources. The research results provide evidence for the prediction of oil and gas reservoirs.

Numerical Investigation on Low-Salinity Augmented Microbial Flooding within a Sandstone Core for Enhanced Oil Recovery under Nonisothermal and pH Gradient Conditions

Summary In an era of increasing energy demand, declining oil fields, and fluctuating crude oil prices globally, most oil companies are looking forward to implementing cost-effective and environmentally sustainable enhanced oil recovery (EOR) techniques such as low salinity waterflooding (LSWF) and microbial EOR (MEOR). The present study numerically investigates the combined influence of simultaneous LSWF and microbial flooding for in-situ MEOR in tertiary mode within a sandstone core under spatiotemporally varying pH and temperature conditions. The developed black oil model consists of five major coupled submodels: nonlinear heat transport model; ion transport coupled with multiple ion exchange (MIE) involving uncomplexed cations and anions; pH variation with salinity and temperature; coupled reactive transport of injected substrates, Pseudomonas putida and produced biosurfactants with microbial maximum specific growth rate varying with temperature, salinity, and pH; relative permeability and fractional flow curve variations owing to interfacial tension (IFT) reduction and wettability alteration (WA) by LSWF and biofilm deposition. The governing equations are solved using finite difference technique. Operator splitting and bisection methods are adopted to solve the MIE-transport model. The present model is found to be numerically stable and agree well with previously published experimental and analytical results. In the proposed MIE-transport mechanism, decreasing injection water (IW) salinity from 2.52 to 0.32 M causes enhanced Ca2+ desorption rendering rock surface toward more water-wet. Consequently, oil relative permeability (kro) increases with >55% reduction in water fractional flow (fw) at water saturation of 0.5 from the initial oil-wet condition. Further reducing IW salinity to 0.03 M causes Ca2+ adsorption shifting the surface wettability toward more oil-wet, thus increasing fw by 52%. Formation water (FW) salinity showed minor impact on WA with <5% decrease in fw when FW salinity is reduced from 3.15 to 1.05 M. During low-salinity augmented microbial flooding (LSAMF), biosurfactant production is enhanced by >63% on reducing IW salinity from 2.52 to 0.32 M with negligible increase on further reducing IW and FW salinities. This might be owing to limiting nonisothermal condition (40 to 55°C), dispersion, sorption, and microbial decay. During LSAMF, maximum biosurfactant production occurs at microbial maximum specific growth rate of 0.53 h-1, mean fluid velocity of 2.63×10-3 m h-1 and initial oil saturation of 0.6, thus resulting in significant WA, increase in kro by >20%, and corresponding fw reduction by >84%. Moreover, the EOR efficiency of LSAMF is marginally impacted even on increasing the minimum attainable IFT by two orders of magnitude from 10-3 to 10-1 mN m-1. Though pH increased from 8.0 to 8.9, it showed minor impact on microbial metabolism. Formation damage owing to bioplugging observed near injection point causing increase in fw by ~26% can be mitigated by adopting suitable well-stimulation strategies during the LSAMF run time. The present study is a novel attempt to show synergistic effect of LSAMF over LSWF in enhancing oil mobility and recovery at core scale by simultaneously addressing complex crude oil-brine-rock (COBR) chemistry and critical thermodynamic parameters that govern MEOR efficiency within a typical sandstone formation. The present model with relatively lower computational cost and running time improves the predictive capability to preselect potential field candidates for successful LSAMF implementation.

The genesis of authigenic minerals and the porosity evolution of various lithologies and their implications for identifying high-quality reservoirs in the fourth member of Xujiahe Formation (Northeast-Sichuan Basin, China)

With petroleum exploration extending to deeper reservoirs, it becomes more and more difficult to find relatively high-quality reservoirs in heterogeneous sandstones. This research integrates fluid inclusion analysis, petrographic, mineralogical, and geochemical data to determine the origin of authigenic minerals, establish the porosity evolution model and discuss diagenetic effects on reservoir quality of the fourth member of the Upper Triassic Xujiahe Formation. The main rock types of studied sandstones are identified by thin-section, SEM and XRD analysis-feldspathic litharenites, litharenites, calcareous sandstone and chlorite-rich sandstone. Of the four types of sandstone, reservoir porosity of the chlorite-rich sandstone is generally the highest. Target sandstones have experienced complicated diagenetic histories including mechanical compaction, three stages of carbonate cementation, the dissolution of K-feldspar or rock fragments, three kinds of authigenic chlorite precipitation, and two stages of quartz precipitation. Two reaction pathways between K-feldspar and kaolinite were determined and limited dissolution was generated in the closed diagenetic system. Diagenetic sequence and porosity evolution suggest that the critical factors in reducing reservoir quality can be attributed to early intense compaction and widespread calcite cementation. The genesis of high-quality reservoirs among the various lithologies is different. In feldspathic litharenites and litharenites, the key factors for the development of relatively high-quality reservoirs is the acidic dissolution of K-feldspar and less cement being present in the rock. Because chlorite helps retain primary pores by inhibiting quartz overgrowths, almost all chlorite-rich sandstone are relatively high-quality reservoirs. In general, the reservoir quality of calcareous sandstone is poor unless fractures exist that can improve permeability. Determining the porosity evolution of various lithologies is an effective method to predict relatively high-quality reservoirs, which can provide a useful reference for deep petroleum exploration in other areas.

Recovery Observations from Alkali, Nanoparticles and Polymer Flooding as Combined Processes.

We have studied wettability alterations through imbibition/flooding and their synergy with interfacial tension (IFT) for alkalis, nanoparticles and polymers. Thus, the total acid number (TAN) of oil may determine the wetting-state of the reservoir and influence recovery and IFT. Data obtained demonstrate how the oil TAN number (low and high), chemical agent and reservoir mineralogy influence fluid–fluid and rock–fluid interactions. We used a laboratory evaluation workflow that combines complementary assessments such as spontaneous imbibition tests, IFT, contact angle measurements and selected core floods. The workflow evaluates wettability alteration, IFT changes and recovery when injecting alkalis, nanoparticles and polymers, or a combination of them. Dynamics and mechanisms of imbibition were tracked by analyzing the recovery change with the inverse bond number. Three sandstone types (outcrops) were used, which mainly differed in clay content and permeability. Oils with low and high TANs were used, the latter from the potential field pilot 16 TH reservoir in the Matzen field (Austria). We have investigated and identified some of the conditions leading to increases in recovery rates as well as ultimate recovery by the imbibition of alkali, nanoparticle and polymer aqueous phases. This study presents novel data on the synergy of IFT, contact angle Amott imbibition, and core floods for the chemical processes studied.

Effect of supercritical CO2 flooding on the produced water quality and performance of the scale inhibitors in a typical tight sandstone oilfield

In order to enhance oil recovery, supercritical CO2 (scCO2) flooding has been applied in many oilfields to extract oil and gas post primary recovery. However, it causes serious scaling problems in the reservoir, oil well and production tubing. In this article, the produced water quality before and after scCO2 flooding in carbonate reservoirs are analyzed. The scaling trend of produced water before and after scCO2 flooding was calculated by using the Davis-stiff saturation index and Ryznar stability index methods. Static experiments and scanning electron microscope (SEM) are used to study the scale inhibition performance and mechanism of HEDP, ATMP, MA-AA, and PAA on CaCO3 in produced water before and after scCO2 flooding. The results show that after scCO2 flooding, the quality of produced water changes obviously, thus the scaling trend of produced water increases, the growth of CaCO3 crystal is affected and the scale inhibition efficiency of conventional scale inhibitors decreases.

Monitoring geological storage of CO2 using a new rock physics model

To mitigate the global warming crisis, one of the effective ways is to capture CO2 at an emitting source and inject it underground in saline aquifers, depleted oil and gas reservoirs, or in coal beds. This process is known as carbon capture and storage (CCS). With CCS, CO2 is considered a waste product that has to be disposed of properly, like sewage and other pollutants. While and after CO2 injection, monitoring of the CO2 storage site is necessary to observe CO2 plume movement and detect potential leakage. For CO2 monitoring, various physical property changes are employed to delineate the plume area and migration pathways with their pros and cons. We introduce a new rock physics model to facilitate the time-lapse estimation of CO2 saturation and possible pressure changes within a CO2 storage reservoir based on physical properties obtained from the prestack seismic inversion. We demonstrate that the CO2 plume delineation, saturation, and pressure changes estimations are possible using a combination of Acoustic Impedance (AI) and P- to S-wave velocity ratio (Vp/Vs) inverted from time-lapse or four-dimensional (4D) seismic. We assumed a scenario over a period of 40 years comprising an initial 25 year injection period. Our results show that monitoring the CO2 plume in terms of extent and saturation can be carried out using our rock physics-derived method. The suggested method, without going into the elastic moduli level, handles the elastic property cubes, which are commonly obtained from the prestack seismic inversion. Pressure changes quantification is also possible within un-cemented sands; however, the stress/cementation coefficient in our proposed model needs further study to relate that with effective stress in various types of sandstones. The three-dimensional (3D) seismic usually covers the area from the reservoir's base to the surface making it possible to detect the CO2 plume's lateral and vertical migration. However, the comparatively low resolution of seismic, the inversion uncertainties, lateral mineral, and shale property variations are some limitations, which warrant consideration. This method can also be applied for the exploration and monitoring of hydrocarbon production.

Evaluation of pore-scale wettability in the tight sandstone reservoirs of the Upper Triassic Yanchang Formation, Ordos Basin, China

Wettability is a key factor influencing multiphase fluid distributions and flow behavior in the reservoirs. The microscopic characteristics of the mixed wettability which is a special wettability type are unclear in sandstone reservoirs. An integrated study of petrographic, petrophysical and pore-scales wettability by Environmental Scanning Electron Microscope (ESEM) using the water condensation method were carried out on typical sandstone samples in the Chang-6 interval of Yanchang Formation, southeastern Ordos Basin, and the characteristics of mixed wettability were investigated. It shows that the oil-free sandstones are water-wet in general, while the oil-bearing sandstones are apparently mixed-wet. In the mixed-wet sandstones, the walls of different pores or even the same one pore display different wetting states. The mixed wetting nature of the tight sandstones was probably caused by the early phase oil charge. After oil charged into the reservoir, chlorite surfaces in contacting with pores adsorbed the polar compounds in the crude oil, and their wettability was altered locally from water-wet to oil-wet states. However, pore walls surrounded by quartz and feldspars mainly remained water-wet after oil charge.

Occurrence of uranium minerals in the Xiaomeigou Formation in northern Qaidam Basin, Northwest China

The Lenghu sandstone type uranium deposit as industrial value in the northern Qaidam Basin, Northwest China. This study analyzed the LA-ICP-MS U-Pb dating of detrital zircons, mineralogical features, electron probe, backscatter electron imaging and track etch of the altered minerals from uranium-bearing strata in the Xiaomeigou Formation of Lower Jurassic on the basis of field investigation in order to trace the source, parent rock lithology, geochronological age, uranium minerals, compositional characteristics, occurrences of uranium mineralization.The U-Pb ages of detrital zircons from the ore-bearing member are ranging from 117 to 270 Ma and 370–480 Ma, respectively, indicating that the provenance and uranium source were mainly derived from the Permian-Triassic intermediate-acid igneous rocks in the eastern Altyn Tagh and western Saishiteng Mountains, a small amount of them are from the Ordovician-Silurian intermediate-acid igneous rocks in the Xiaosaishiteng Mountains. Two types of ores in Xiaomigou Formation in Lenghu region are mainly composed of graywacke and carbonaceous sandstone with main uranium minerals are coffinite, pitchblende and trace amounts of lead selenite. They are closely associated with clay minerals, organics and pyrite, which lie in the intergranular space of quartz, feldspar and other altered lithic mineral grains or in cleavage joints of altered clay minerals that occur in fine columnar, gel-like or irregular sawtooth shape. It is inferred that the Fe2+ in feldspar and biotite reacts with H2S or S2- bearing minerals participated in the formation of pyrite, where the U6+ was captured by late multiple fluid processes occurred reduction-precipitation-adsorption uranium mineralization in the reduction environment provided by Fe2+. Based on the analysis of the existence of high Y and low Y types of uranium minerals, it is inferred that uranium in uranium minerals is the residual of original uranium minerals derived from the pre-enrichment of uranium-bearing detrital particles in sedimentary and diagenetic stages, and at the later stage, the high radioactivity abnormal geological bodies migrated to the inner basin through the multi-stage reformation of uranium-containing and oxygen-containing fluids without Y or at very low contents.

Characteristics of heterogeneous diagenesis and modification to physical properties of Upper Paleozoic tight gas reservoir in eastern Ordos Basin

To correctly evaluate reservoir quality and determine promising tight gas zones, the characteristics of heterogeneous diagenesis and modifications to physical properties in the Upper Paleozoic tight gas reservoir in the eastern Ordos Basin (UPTGREOB) were assessed by comprehensively analyzing lithology, petrophysics, and organic geochemistry data. It was found that the types of sandstones in UPTGREOB mainly include (feldspathic) detritus sandstones and detritus feldspathic sandstone in low–ultralow porosity and permeability, with complex pore structure. Sandstone pores can be divided into two types: primary (primary intergranular and residual primary intergranular pores), secondary (intercrystalline, dissolved intragranular, dissolved intergranular, and dissolved cementing pores and microfractures). The main types of diagenesis are compaction, cementation, dissolution, and metasomatic alteration. Shiqianfeng Formation and Upper Shihezi Formation belong to period B of the syndiagenesis stage and period A1 and A2 of the mesodiagenesis stage; Lower Shihezi Formation and Shanxi Formation are entirely in the mesodiagenesis stage; Taiyuan Formation can be regarded to be in periods A2 and B of the mesodiagenesis stage and period A of the telodiagenesis stage. The original porosity of UPTGREOB was approximately 34%. Compaction was the primary destructive diagenesis rather than cementation, while dissolution was found to be the primary constructive diagenesis. The heterogeneous diagenesis played different roles in the UPTGREOB: in syndiagenesis B, the UPTGREOB began to densify under the compaction and early cementation; in mesodiagenesis A, dissolution and metasomatic alteration produced massive secondary dissolved pores and intercrystalline pores, improving the porosity and permeability; in mesodiagenesis B, dissolved pores were filled by new cements, resulting in decreased porosity and permeability; in telodiagenesis A, intensified compaction and cementation made the UPTGREOB retain extra low porosity and permeability. In general, the reservoirs of Shiqianfeng Formation and Upper/Lower Shihezi Formation in the mesodiagenesis stage A have preferable physical properties for tight gas accumulation.

Optimization of management measures for water-producing gas wells in SM gas field

SM gas field is a typical tight sandstone gas reservoir, which adopts the production mode of downhole throttling and inter-well series connection. Gas wells will have different production characteristics at different stages of production, which will cause the management measures implemented by gas wells in different stages to have different effects on efficiency[1-2]. Based on the complex production law of water-producing gas wells in SM Gas Field, this paper is based on the quantitative evaluation of the impact of water production on gas well development indicators for the latter. Clarify the reasons for the production of water and water from gas wells, understand the production rules of water-producing gas wells, optimize the management measures of water-producing gas wells in SM Gas Field, and clarify the rational production allocation methods and work under various complex water-producing conditions during the development of water-producing gas wells system[3]. It can also lay a foundation for the subsequent development of low-yield and low-efficiency wells to tap potential measures, to propose technical countermeasures to enhance oil recovery in the SM gas field, and to carry out gas field-related stable production potential evaluation.

Dynamic Mechanical Characteristics of Impact Rock under the Combined Action of Different Constant Temperatures and Static and Dynamic Loads

The complex mechanical environment of deep coal and rock masses leads to obvious changes on their dynamic mechanical properties. However, there are few reports on the dynamic mechanical properties of rocks under the combined action of medium temperature (normal temperature ∼100°C) and static and dynamic loads. In this paper, a dynamic load and temperature combined action Hopkinson pressure bar experimental system is used to experimentally study the impact type of a fine sandstone under temperature conditions of 18°C, 40°C, 60°C, 80°C, and 100°C, an axial static load of 3 MPa, a gas chamber pressure of 0.06 MPa, and a constant temperature time of 4 h. The dynamic characteristics of the change law of the fine sandstone and the energy dissipation characteristics of the load process are analyzed, and the characteristic law of the fine sandstone surface response is analyzed using digital image correlation technology. Our results indicate the following. (1) Under conditions in which the other experimental conditions remain unchanged, the dynamic stress-strain of the fine sandstone presents a bimodal shape with a “rebound” phenomenon. Increasing temperature causes the peak strength of the fine sandstone to increase; however, the relative strength can increase or decrease. The relative increase in the strength is 1.14 MPa (°C) when the temperature increases from 40°C to 60°C, 0.15 MPa (°C) when the temperature increases from 60°C to 80°C, and 0.62 MPa (°C) when the temperature increases from 80°C to 100°C. (2) The digital image correlation results show that, under the action of a dynamic load stress wave, the fine sandstone experiences a displacement vector change on the sample surface; furthermore, under the combined action of the temperature and dynamic and static loads, the fine sandstone experiences macroscopic shear failure. The surface strain in the propagation direction of the stress wave is obviously higher and can even reach values of more than 10 times that of the strain in other directions. (3) From the perspective of energy dissipation, the incident energy, reflected energy, and dissipated energy of the fine sandstone under an impact load have the same change law. After being affected by a dynamic load, the energy rapidly increases to a certain value and then remains relatively stable. The transmitted energy is relatively small and can be approximated as a horizontal line. As the temperature increases, the incident energy, reflected energy, and dissipated energy tend to first decrease and then increase, and most of the incident energy in the fine sandstone is dissipated in the form of reflected waves.

Research on the relationship between anti-skid performance and various aggregate micro texture based on laser scanning confocal microscope

The micro-texture of the aggregate plays a very important role in the anti-skid performance of the asphalt pavement. Currently, the polished stone value (PSV) index is mostly used for the characterization of the aggregate, but the micro-texture is rarely considered. In addition, there are few studies that compares micro-textures of different aggregates and their relationship with PSV. In this study, eight different aggregates were selected, including three types of sandstone, limestone, basalt, diabase, gabbro and granite. The PSV and micro-texture of the aggregates during the polishing process were tested by the british pendulum tester (BPT) and the laser scanning confocal microscope (LSCM) respectively, and the relationship between PSV and the micro-texture was regressed. Finally, scanning electron microscope (SEM) images were generated and used to explain the reason for the texture differences in the aggregate from the perspective of the micro-structure. It was found that there was no significant difference on the anti-skid performance of the aggregates before polishing. SEM images showed an unevenness on the surface of sandstone with lots of pits, which is conducive for long-term maintenance of texture. Consequently, sandstone had the best anti-skid performance after polishing, followed by magmatic rock, and limestone. Although, polishing effect reduces the micro-texture of the aggregates, but the micro-texture of the sandstone aggregate was not significantly affected before and after polishing. Overall, the texture of arkose was the largest, followed by red sandstone, quartz sandstone, granite, diabase, gabbro, basalt, limestone. There is an obvious correlation between the micro-texture and the anti-skid performance of the aggregate. The aggregates had better anti-skid performance when the micro-texture index Ra was kept above 4 μm. The multiple linear equation between micro-texture and PSV is obtained by regression analysis, which can be used to predict the PSV of the aggregate. Based on the findings from this study, sandstone is highly recommended as the first choice aggregate for anti-skid performance, followed by magmatic rock and finally limestone.

Bi-Fractal Characterization of the Pore Network of Tight Sandstone

Fluid seepage performance and accumulation in tight sandstone is a critical research topic for in-depth exploration and development, closely related to the heterogeneity of the pore network. The fractal characterization is one of the most compelling and direct ways for quantitative investigation of heterogeneity. However, only one kind of fractal is used in most studies, and the differences and relations between different fractal dimensions are rarely discussed. This paper chose one of the most representative tight sandstone formations in China, the second member of the Xujiahe Formation, as the research object. First, based on physical analysis and XRD analysis, we carried out a qualitative investigation on pore structure utilizing thin-section and scanning electron microscopy. Then, detailed pore structure parameters were obtained using high-pressure mercury intrusion (HPMI). Lastly, we combined two-dimensional fractal analysis on thin-section images and three-dimensional fractal analysis on HPMI data to characterize the pore network heterogeneity quantitatively. The Xu2 tight sandstone is mainly medium- to fine-grained lithic feldspathic sandstone or feldspathic lithic sandstone with low porosity and permeability. Also, the Xujiahe tight sandstone is mainly composed of quartz, feldspar, and clay. The pore types of Xu2 tight sandstones are primarily intergranular pores, micro-fractures, and intra- and intergranular dissolution pores. Moreover, most of the micro-fractures in gas-bearing formation are open-ended, while most are filled by clay minerals in the dry formation. The r50 (median pore radius) is the most sensitive parameter to seepage capability (permeability) and gas-bearing status. The 2D fractal dimension (Ds) of gas-bearing samples is significantly larger than that of dry samples, while the 3D fractal dimension (D1, D2) of gas-bearing samples is lower than that of dry samples. There is a strong negative correlation between D2 and gas-bearing status, permeability, quartz content, and r50, but a positive correlation between Ds and these parameters. D2 represents the heterogeneity of pore space, while the Ds indicates the development of the pore network. Tectonic movements that generate micro-fractures and clay cementation that blocks the seepage channels are the two main controlling factors on fractal dimensions. Combining 2D and 3D fractal analysis could give a more in-depth investigation of pore structure.