查看更多>>摘要：In order to study the salinity of fracturing fluid flowback from shale gas wells and its damage to reservoirs, shale gas wells in PS (Peng Shui) and CN (Chang Ning) areas of Sichuan Basin (China) were taken as research objects in the current work. Immersion experiments of shale particles and single mineral particles were carried out using distilled water. The conductivity of distilled water during immersion was monitored using a conductivity meter, and the ionic composition and the content of immersed fluid were analyzed using ion chromatograph and atomic absorption spectrophotometer. Meanwhile, the flowback fracturing fluids from shale gas wells in PS and CN areas of Longmaxi reservoir in Sichuan Basin, China were collected, and their salinity and composition were analyzed. The results of shale particle immersion experiments showed that the mass concentration of salt in shale was 1 mg salt/g of shale. Furthermore, the salinity of flowback fracturing fluid was found to be about 30,000 mg/L. Compositional analyses of shale particle immersion fluid and field flowback fluid show that the contents of Na+ and Cl in shale reservoir are the highest. The analysis of field flowback fracturing fluid in shale gas wells shows that the salinity of flowback fracturing fluid is much higher than that of fracturing fluid. High salinity flowback fracturing fluid would produce salt crystals in the later stage of flowback and production stage, blocking fractures and pores, and reducing gas seepage capacity.
查看更多>>摘要：Perforation is critical to create a flow pathway between a shale reservoir and the production casing for hydraulic fracturing. However, the damage characteristics of shales by abrasive waterjet (AWJ) remain unclear. To address this concern, AWJ experiment is conducted for three types of shale with different mineral compositions, including siliceous shale, calcareous shale, and carbonaceous shale. X-ray diffractometry measures the content of mineral components. A rock mechanics test system obtains the main physical and mechanical parameters of shale samples. Scanning electron microscope (SEM) and acoustic emission (AE) are used to analyze the damage characteristics. The results indicate that siliceous shale with more brittle minerals is beneficial for the AWJ to create a larger perforation effectively, while carbonaceous shale with more clay minerals significantly lowers AWJ performance. For the shale with more brittle minerals, abrasive erosion and matrix spallation govern shale failures. As the clay content increases, the primary rock damage is abrasive cutting leading to the transgranular fracture. AE signals induced by AWJ impact could reflect breaking mechanisms and identify the difference in shale lithology. The energy dissipation gradually reduces during the AWJ process. Also, the dissipation has a negative linear correlation with the content of brittle minerals. This study provides fundamental insight into understanding shale damage by AWJ impact to optimize the perforation scheme.
查看更多>>摘要：The shape of ore body in deep underground engineering is complex, and its fracture development degree is affected by water abundance, fracture zone, fault and other factors. With the deepening of depth, the vertical and horizontal stress changes significantly, which has a great impact on the fracture opening. Therefore, the fracture dip angle and its three-dimensional stress state are the main factors affecting the fluid flow of fractures in a large area of ore body and its hanging and footwall rock mass. In this study, firstly, the three-dimensional fractal dimension of a single-fracture specimen was obtained by using CT (Computer Tomography) scanning technology and the single-fracture specimen with a similar three-dimensional fractal dimension was selected for testing. Then, the self-developed single fracture stress seepage coupling true triaxial test system is applied to test the seepage of single fracture samples with six different fracture dip angles under different stress states of underground depth. The experimental results show that the fluid flow and strain of fractured rock mass are comprehensively affected by the fracture dip angle and the stress state of the underground depth, and the influence degree of the fracture dip angle changes with the deepening of the underground depth. The above conclusions can be mutually verified in the aspects of stress-strain, water pressure and permeability coefficient. Furthermore, the relationship between the minimum injectable water pressure (MIWP) of fractured rock mass with different dip angles and underground depth is obtained, the expression of seepage coefficient of single fracture specimen with different dip angles and underground depth under three-dimensional stress is summarized, and the relationship between eh and em of single fracture specimen with different fracture dip angles is determined. This study provides a basic reference for the design scheme of hydraulic conductivity of fractured zone or fractured rock mass with different underground depths.
查看更多>>摘要：The main objective of this study is to design and apply surface-functionalized Fe3O4 particles to reduce the viscosity of heavy oil from Shengli Oilfield and to study the mechanism of viscosity reduction. Fe3O4 particles were synthesized by the co-precipitation method and modified with 3-propyl trimethoxysilane (KH570), oleic acid (OA), and triethoxyvinylsilane (A151) to obtain Fe3O4-KH570, Fe3O4-OA, and Fe3O4-A151, respectively. The particles were characterized through Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), and Dynamic Light Scattering (DLS). The contact angle and dispersion stability in kerosene were evaluated. The average net degree of viscosity reduction (%DVR) of Fe3O4-KH570, Fe3O4-OA, and Fe3O4-A151 on Chenping heavy oil at 50 degrees C is 27.91%, 51.27%, and 29.44%, respectively. The surface functionalization of asphaltene aggregates, the improvement of lipophilicity, and dispersion stability after destruction are the main reasons for the decrease of heavy oil viscosity. Particle size and the ability to adsorb asphaltenes have no direct relationship with DVR. It was also confirmed that the modified Fe3O4 particles can effectively recycle from the oil under a magnetic field. This work developed a kind of recyclable Fe3O4 particles for heavy oil viscosity reduction, which was beneficial to lower the cost in heavy oil recovery.
Nam Nguyen Hai LeSugai, YuichiVo-Thanh, HungNguele, Ronald...
14页
查看更多>>摘要：To further improve carbon dioxide enhanced oil recovery CO2-EOR efficiency in heterogeneous reservoirs, the use of CO2 microbubbles as a temporary blocking agent is attracting widespread interest due to their significant stability. This study aims to investigate the plugging performance of CO2 microbubbles in both homogeneous and heterogeneous porous media through a series of sandpack experiments. First of all, CO2 microbubble fluids were generated by stirring CO2 gas diffused into polymer (Xanthan gum (XG)) and surfactant (Sodium dodecyl sulfate (SDS)) solution with different gas: liquid ratios. Then, CO2 microbubbles fluids were injected into single-core and dual-core sandpack systems. The results show that the rheological behaviors of CO2 microbubble fluids in this study were followed the Power-law model at room temperature. The apparent viscosity of CO2 microbubble fluid increased as the gas: liquid ratio increased. CO2 microbubbles could block pore throat due to the "Jamin effect" and increase the resistance in porous media. The blocking ability of CO2 microbubbles reached an optimal value at the gas:liquid ratio of 20% in the homogeneous porous media. Moreover, the selective pugging ability of CO2 microbubbles in dual-core sandpack tests was significant. CO2 microbubbles exhibited a good flow control profile in the high permeability region and flexibility to flow over the pore constrictions in the low permeability region, leading to an ultimate fractional flow proportion (50%:50%) in the dual-core sandpack model with a permeability differential of 1.0:2.0 darcy. The fractional flow ratio was considerable compared with a polymer injection. At the higher heterogeneity of porous media (0.5:2.0 darcy), CO2 microbubble fluid could still establish a good swept performance. This makes CO2 microbubble fluid injection a promising candidate for heterogeneous reservoirs where conventional CO2 flooding processes have limited ability. This finding would be helpful in developing the utilization of CO2 microbubbles in EOR operation by better understanding their plugging mechanism in porous media.
查看更多>>摘要：Appraisal well testing plays a key role in optimizing a complex field's exploitation strategy - and increasing complexity often calls for more elaborate reservoir models for the proper interpretation of each test's results. The classical analytical methods usually require restrictive simplifying assumptions, which limit their usefulness when dealing with reservoir heterogeneity. We seek to solve this issue by applying the hybrid analytical-numerical Generalized Integral Transform Technique (GITT) to the pressure diffusivity equation - and specifically, to the point-source problem extended to a reservoir with arbitrary permeability variation irregularly distributed throughout the 3D domain. The technique is first demonstrated to produce an exact alternative form of the well-known solution to the classical point-source in a homogeneous reservoir. This equivalence is then used to derive a computationally efficient working expression for the generalized point source in a heterogeneous reservoir. Finally, this building block is applied to construct a uniform flow solution for a limited entry vertical well through spatial superposition - thus demonstrating the usage of the GITT for other wellbore geometries. Synthetic examples are used to show that the obtained expressions are in good agreement with results from a commercial reservoir simulator. In all cases presented, the eigenfunction expansions for both the drawdown pressure and its logarithmic derivative converge to at least four and two significant digits, respectively, within the adopted practical ranges of the series' truncation orders. It is clear that the pressure expansions have better convergence characteristics, which are also influenced by the time value and by the distance from the position under consideration to the point-source. The resulting novel solution to the point-source provided in the present work is the most general and least restrictive expression presented so far to this single problem in a heterogeneous domain, and it is suitable for pressure transient analysis.
查看更多>>摘要：In view of the differential productivity of coalbed methane (CBM) wells in the Linfen block on the southeastern margin of the Ordos basin, geochemical analysis is performed to determine the hydrodynamic condition of coal reservoirs, identify the water and gas source of commingled wells, reveal different pressure drop mechanisms, and finally clarify the geological and engineering controls on the production performance. The positive correlations between average daily gas production and the concentrations of Na+, Cl-, TDS, Sr, and Ba imply that strong hydraulic closure is the premise of high productivity. There is no obvious relationship between water and gas production. Commingled (5 + 8#) wells tend to produce more water than single-layered (5#) wells, because the No. 8 coal seam has more active hydrodynamic condition, which is proven by the lighter delta H-2 and delta O-18 and smaller Sr/Ba ratio of waters from commingled wells. The difficulty in pressure drop funnel expansion is the primary constrains for the single-layered wells, which is only resolved by the horizontal wells located in low structural positions at present characterized by increasing trends of TDS, Na+ and Cl- contents during drainage. The faster the ion concentration rises, the faster the pressure drop funnel expands and a high peak daily gas production can be quickly achieved. The L-shaped horizontal well is thought to be the most suitable well type due to its high gas yield, low time investment and engineering cost. Due to hydrodynamic heterogeneity, commingled wells often show strong interlayer interference and a change in the water-producing horizon from 5# to 8# coal, which is manifested in the tendency of Cl-, Na+, and TDS to increase first and then decrease. By selecting superior lithologic assemblages and avoiding strong aquifers, relatively continuous and stable production of commingled wells can also be achieved. This study provides a basis for the further development of CBM in the Linfen block and enriches engineering geochemistry theory.
查看更多>>摘要：The numerical simulation of matrix acidization in fractured porous media is continuous work in the reservoir simulation community. However, existing works mainly depend on two kinds of models to describe fractured porous media: the discrete fracture-matrix (DFM) model and the continuum fracture (CF) model. In addition, most of the works use Darcy's equation to describe the flows. The DFM model can accurately describe the fracture and the flow in the fracture at the cost of the complexity of the simulation framework. On the other hand, the CF model treats the fracture and the matrix uniformly, which reduces the complexity of the simulation framework, but the accuracy of the results is not as good as that of the DFM model. In summary, the challenge of this area is that the accuracy of the results cannot be guaranteed by a sufficiently simple model. The DarcyBrinkman-Forchheimer (DBF) framework was originally developed to handle an issue in matrix acidization simulation, i.e., the flows in the high-porosity zones cannot be well described by Darcy's law. Considering the similarity of the fracture and the high-porosity zones, it is anticipated that the proposed DBF framework can also describe the flows in the fracture well., i.e., the accuracy of the results guaranteed by the DFM model can also be guaranteed by the DBF framework. Compared with the DFM model, the DBF framework is much simpler. Moreover, the DBF framework can be naturally integrated with the CF model. Thus, this work leverages the CF model and the DBF framework to simulate matrix acidization in fractured porous media, by which accurate results can be achieved with a simple simulation framework. The simulation results in this work are compared with those of Khoei's work, by which the reasonability of this work is demonstrated. After that, the thermal DBF framework, which is an expansion of the DBF framework, is leveraged to investigate matrix acidization in fractured porous media under different thermal conditions, and many helpful conclusions that benefit realistic operations are drawn. For example, the fracture orientation can have different effects on matrix acidization under different temperature conditions.
查看更多>>摘要：Significant fracture conductivity can be achieved using a much lower material cost based on the optimal partial-monolayer proppant concentration (OPPC) theory. However, experimental validation and investigation of the OPPC theory have been extremely rare in the literature. In this study, we used a laboratory fracture conductivity cell to conduct well-controlled fracture conductivity experiments to comprehensively study the role of effective stress, proppant size, rock type, and water soaking on the evolution of fracture conductivity as a function of increasing proppant concentration. With seven proppant concentrations (up to 2 lb/ft(2)) and seven effective stresses (up to 6000 psi) used in the conductivity measurements, we experimentally confirmed that the correlation between fracture conductivity and proppant concentration was non-monotonic because of a competing process between fracture permeability and fracture width. We also investigated the influence of the abovementioned experimental conditions on the OPPC and the corresponding optimal fracture conductivity (OFC). This is the first study that uses well-controlled laboratory experiments to comprehensively investigate nonmonotonic fracture conductivity evolutions. The existence of the OPPC indicates that a relatively low proppant amount can be used to form a partial-monolayer proppant pack in the fracture space, which has similar or higher fracture conductivity compared to a multilayer proppant structure. This finding has important economic implications because high-strength, ultralight-weight proppant particles can be used to form partial-monolayer proppant packs in fractures, leading to sufficiently high fracture conductivity using a much lower material cost compared to multilayer proppant structures. Our experiments illustrated that proppant embedment is the primary mechanism that causes the competing process between fracture width and fracture permeability and consequently the non-monotonic fracture conductivity evolution as a function of increasing proppant concentration. Without proppant embedment, there will not be such a competing process, and the non-monotonic fracture conductivity evolution will not be observed.
查看更多>>摘要：To better understand the effect of the pore-fracture dual-porosity structure on the coal permeability, the methods for calculating the pore size distribution as well as the fracture width distribution based on the Euclidean distance map function were given first. On this basis, a permeability estimation model considering pore-fracture structure was derived. Then, the pore-fracture structure and permeability of coal samples were quantitatively analyzed by scanning electron microscopy (SEM). By considering the pore size distribution and fracture width distribution characteristics separately, the complex pore structure of the coal sample can be more clearly defined. We found that both pores and fractures have their own distribution characteristics, but due to the effect of resolution, there is some influence in quantifying the minimum size distribution, especially in quantifying the pore size distribution. In predicting the permeability, the direct calculation using the pore and fracture size distribution is significantly larger than the experimental results (1.18 x 10(-)(14) m(2) vs. 6.9 x 10(-16) m(2) (measured) for the A1 and 1.22 x 10(-)(14) m(2) vs. 8.1 x 10 -16 m(2) (measured) for the A2 at x 1000 magnification). However, by further considering the effect of tortuosity, more accurate prediction results can be obtained (1.14 x 10(-16) m(2) for the A1 and 1.22 x 10(-15) m(2) for the A2 at x 1000 magnification). Fractures occupy less space, but they would cause higher permeability. The method proposed in the current study can be further applied to quantify the pore-fracture structure and permeability characteristics in microgeology.
NSTL
Elsevier