查看更多>>摘要：Horizontal well with subdivision cutting fracturing technology is a new technical way to improve the efficient development of shale reservoirs. Subdivision cutting fracturing has the characteristics of stronger inter-fracture interference, more variable parameters and constraints. This fracturing technology has no efficient method to optimize the discrete and continuous fracture parameters integrally. A new automatic integrated optimization algorithm is proposed. The algorithm adopts the SPSA nested binary search algorithm to optimize the discrete and continuous fracture parameters. Considering the flow mechanism of multi-scale media in shale reservoirs, a numerical flow simulation model of subdivision cutting fractured horizontal wells is established. Then, taking the NPV as the objective function, a multi-parameter integrated optimization model is established. Make the method apply to a typical test shale reservoir. The optimization results show that the NPV of the optimum fracture parameter combination is 37.69%-57.36% higher than that of the uniform fracture distribution combination. And the optimum fracture combination presents a spindle-like distribution. This method is applied to an actual shale reservoir in Xinjiang to verify the broad application. The fracture parameter combination of two parallel horizontal wells in the reservoir is optimized. The optimization results show that the NPV has been dramatically improved, with an increasing range of 37.94%-96.84%. And the fractures of two adjacent horizontal wells present zipper staggered distribution. The integrated optimization method of fracture parameters can provide theoretical guidance for hydraulic fracturing design.
Tian, JieWang, LiangZhao, Rong RongLiu, Hong Qi...
10页
查看更多>>摘要：Porosity exponent (m) is a key parameter for calculating reservoir oil and gas saturation and evaluating reservoir effectiveness; the development of matrix pores, vug pores, and fractures makes the m response regularity of fractured-vuggy reservoirs unclear, which makes the accurate calculation of saturation difficult. By applying Maxwell-Garnett mixing rule to vuggy reservoirs and conductivity tensor analysis to fractured reservoirs, an improved Triple Porosity Model considering fracture dip angle is established. The newly improved Triple Porosity Model clarifies the response regularity of m to the matrix pores, vug pores, fracture pores, and fracture angles. Based on the improved Triple Porosity Model, the response regularity chart of m is further established. The findings show that: (1) m increases with the increase of fracture dip angle (theta) and the development of vugs; (2) m increases with the development of high-angle fractures and decreases with the development of low-angle fractures; (3) in fractured reservoirs, the fracture dip angle of 33 degrees is the critical dip angle that determines the relationship between m and matrix porosity exponent (m(b)); (4) an increase in matrix porosity will weaken the influence of vugs, fractures, and fracture dip angle on m, which will eventually make m converge to m(b). The field application of fractured-vuggy reservoirs shows that the water saturation calculated by the improved Triple Porosity Model is better in agreement with the core analysis results.
查看更多>>摘要：This paper investigates the influence of pore space heterogeneity on the adsorption dynamics in a single-phase flow. The sensitivity of adsorption dynamics to changes in heterogeneity, which is numerically described by the disorder parameter, is studied in combination with the Peclet number, porosity, adsorption rate constant, and absolute permeability. The focus is on applied results that are useful, for example, in chemical and petroleum engineering. The main findings of this paper were obtained in mathematical modeling based on lattice Boltzmann equations (LBE) for fluid flow (MRT collision scheme) and mass transfer processes (SRT collision scheme). Mass transfer at the adsorbent/adsorbate interface is described using the kinetics law of Langmuir adsorption. Numerical simulations are performed on digital images of the porous structures generated using Monte-Carlo's movement method, which controls the pore space heterogeneity. In this work, special attention is paid to the choice of the relaxation parameter in LBE for mass transfer, which affects the adsorption dynamics. The results of this paper show that heterogeneity significantly affects the dynamics of the adsorbed amount. An increase in the disorder parameter leads to a decrease in the velocity of the concentration front and a slowdown in the adsorption rate. It was found that the sensitivity of the dynamics of adsorption to a change in heterogeneity is maximum at low Peclet numbers. The impact of the disorder on adsorption significantly decreases with an increase in the Peclet number. With the prevalence of the convection mechanism, the adsorption dynamics is practically unaffected by heterogeneity. The effect of heterogeneity is most pronounced at low porosity and decreases significantly with its growth. At high porosity, the influence of heterogeneity on the adsorption dynamics was not revealed. The Damkohler number affects the sensitivity of the adsorption dynamics to changes in pore space heterogeneity. The effect of heterogeneity increases with the increasing intensity of mass transfer. In addition, it was found that absolute permeability does not affect adsorption.
查看更多>>摘要：The flow mechanism between the injector and producer is different from the flow in the steam chamber in the Steam-Assisted Gravity Drainage (SAGD) process. The interwell flow between the injector and producer is determined by both gravity and the pressure difference. In this study, the interwell flow model is improved by introducing a relative permeability model and an oil viscosity linearity assumption, considering the availability of input data. The interwell flow in the liquid pool is coupled with the gravity drainage in the steam chamber throughout the entire SAGD process. And the liquid level calculated by the new model is validated by field data. The results show that the subcool gradient is larger in the earlier stage and smaller in the later stage. The liquid level, subcool, pressure difference and wellbore liquid rate are interacted and should be matched to each other. In field applications, the subcool should be controlled differently according to its development stage. The subcool of the hottest spot should be near zero to maximize the well productivity and the steam chamber supply capacity. The results of this study provide theoretical guidance for the evaluation and adjustment of field dual-horizontal SAGD well pairs.
查看更多>>摘要：Source rocks and oil sands from the northern Dongpu Depression have been analyzed by gas chromatography multicollector inductively coupled plasma mass spectrometry (GC-MC-ICP MS) to investigate the compound-specific sulfur isotope (delta S-34) values of saline lacustrine source rocks. The samples were also subject to more traditional organic geochemical analyses including hydrocarbon biomarker detection by gas chromatography/mass spectrometry (GC/MS), carbon and oxygen isotopic analysis by isotope ratio mass spectrometer, and major and trace inorganic element analysis. delta S-34(OSCs) values measured for a limited number of organic sulfur compounds (OSCs) showed a quite large range (5.16 parts per thousand-44.73 parts per thousand). The source rocks and oil sands could be separated into two groups with delta S-34 values above or below 25.00 parts per thousand. The first group with delta S-34 25.00 parts per thousand, were primarily the Weicheng source rocks, which also typically showed an increase in delta S-34 values with increasing alkylation. The second group had delta S-34 < 25.00, the delta S-34 of dibenzothiophenes showed a positive correlation with the concentration of the saturated hydrocarbon fraction of rocks, and a negative correlation with the polar (resin + asphaltene) fraction. The delta S-34(OSCs) show obvious positive correlation with gammacerane/C-31 hopane and C-35/C-34 hopanes and excellent correlation with contents of minerals and ratios of trace elements, reflecting a S-34 enrichment in closed evaporative environment (conducive to the sulfurisation of organic matter) and relative S-34 depletion in terrestrial environments. These trends identify the depositional environment of the source rocks as one of controls on delta S-34(OSCs) values. Thermal maturity was also observed to influence delta S-34(OSCs) values, becoming heavier with increasing maturity. There was a good result of oil-source rock correlation by delta(SOSC)-S-34 in this study. This study demonstrates the contribution delta S-34(OSCs) data can make to oil-oil and oil-source rock correlations as well as providing further evidence of their sensitivity to depositional environments and thermal maturity.
查看更多>>摘要：Condensate banking around wellbores can significantly shorten the production from gas-condensate reservoirs. Several approaches to mitigate this issue have been proposed in the literature, among which gas injection comes out with promising results. This method's efficiency has been largely investigated at core and field scales, but the underlying flow phenomena taking place at the pore-scale are still poorly understood. In order to address this gap, a compositional pore-network model was used to reproduce gas injection in a sandstone sample following condensate accumulation. C-1, C-2, CO2, N-2 and produced gas were tested as the candidates for condensate banking remediation at different pressure levels. After gas flooding, condensate saturation, heavy component recovery and gas relative permeability were quantified to appraise the achieved gas flow improvement. The results indicated that C-2 and CO2 were, overall, the most effective gases to clear the accumulated condensate and re-establish the gas flow. At high pressures, their injection reduced the liquid saturation in the porous medium at least in 80%, and restored gas relative permeabilities to values close to unity. At low pressures, however, no tested gas injection composition could reduce the condensate content in the porous medium more than 30%, contradicting the estimates based solely on liquid dropout curves. With the presented analyses, this work sets out the pioneer efforts towards an accurate pore-scale modeling of miscible gas injection in gas-condensate reservoirs.
查看更多>>摘要：We investigate the injection of a viscoplastic fluid, through an injector, into a channel filled with a lower density Newtonian fluid. The two-dimensional model problem is informed by plug & abandon practices in Western Canada and is analogous to the early stages of the balanced plug method in placing off-bottom plugs (Trudel et al., 2019). We present a systematic study of the effect of the injector size and position on the flow dynamics and fluid accumulation. When the injector and the channel are centralized, an unstable displacement flow develops below the injector. The instability leads to the formation of a mixing layer below the injector that diverts the injected fluid toward the space between the injector and the channel (the gap). The unsteady development of the mixing layer leads to the episodic mixing of the injected fluid that enters the gap. The frequency and magnitude of these contaminated regions change nonmonotonically with the injector width but decrease with the length of the mixing layer. When the injector is not centralized with the channel, the injected fluid flows toward the wide side of the gap. This leads to the formation of a series of vortices below the injector and a relatively short mixing layer. While the fluid that enters the wide side of the gap remains primarily unmixed with the Newtonian fluid, significant periodic mixing is persistent on the narrow side. On the narrow side of the gap, the average degree of mixing of the fluid entering the gap increases significantly with eccentricity while the velocity of the advancing front of the injected fluid decreases. Our results suggest there may be an optimal range of diameter ratios that minimize the mixing of cement slurry and wellbore fluids. In the absence of a mechanical or non-mechanical barrier, the injected fluid may flow toward the gap and accumulate at the target position irrespective of the relative position of the injector within the wellbore. The quality of the accumulated slurry, however, may vary notably with the size and position of the injector.
查看更多>>摘要：The occurrence states (adsorbed or free) directly control the transport and production of shale oil, and free oil is the most common potential product available using existing technologies. A variety of theories and experimental methods have been developed to estimate the adsorbed and free oil amounts in shale pore-fracture systems, however, it is difficult to clarify the microdistribution characteristics of shale oil in in-situ pore systems using these methods. In the study described here, by integrating experimental and theoretical models, an effective method was developed to reveal the microdistribution of oil confined in nanoporous shales from the Dongying Sag, in the Bohai Bay basin, China. Centrifugation-nuclear magnetic resonance (NMR) experiments were com-bined with the modified Langmuir equation, and then applied to estimating amounts of adsorbed and free oil. And the microdistribution characteristics of shale oil were then analyzed by the adsorption ratio theoretical model. Furthermore, the mechanisms of controlling the adsorbed, free amounts and microdistribution of shale oil were also discussed. The primary results demonstrated that the modified Langmuir equation (Langmuir-like equation) was an effective and accurate technique for evaluating the adsorbed and free oil amounts in shales. We estimated that adsorbed and free oil amounts ranged from 5.8023 to 29.7995 mg/g, and from 3.9510 to 25.6410 mg/g, respectively, at a temperature of 20 degrees C, while the adsorbed oil weight ratios were 0.2778-0.7023 (mean 0.5438). The average value of the adsorbed oil density was approximately 2.0231 g/cm(3), which was 2.6994 times that of the free oil. The average adsorbed layer thickness was 0.7433 nm, which equaled nearly two molecular diameters. The adsorbed and free oil microdistribution was clearly described by the adsorption ratio theoretical model and the T-2 spectrum. The adsorbed oil was mainly confined to micropores, while free oil was stored in meso- and macropores-and that pore microstructures affected shale oil microdistribution character-istics. The amount of adsorbed oil was mainly controlled by micropore volume and specific surface area, while the amount of free oil was closely associated with total volume of the larger pores. We also noted that the more complex the pore structure, the lower the free oil content and the higher the adsorption ratio. The amount of adsorbed oil was closely related to the shale composition, and increased with TOC content. The amount (ratio) of adsorbed oil also increased with increasing clay mineral content, and was negatively proportional to the quartz + feldspar content. The authors are confident that the study described in this paper has delivered new insights into the microdistribution of adsorbed and free oil in shale pore-fracture systems.
查看更多>>摘要：The abundant geothermal energy in hot dry rock (HDR) geothermal reservoirs is an attractive renewable energy resource with great potential. Cyclic injection in hydraulic fracturing has been proved to be a suitable way for the geothermal energy exploitation. However, the fracture initiation and propagation regimes induced by cyclic injection have been inadequately studied, and the fracturing optimization for HDR is often by experience. For this reason, true tri-axial hydraulic-fracturing tests were conducted to study the initiation and propagation of hydraulic fractures, while the specimens were subjected to the cyclic injection with different cycle time duration and injection rate. The results revealed that the initiation of hydraulic fracture was displayed as three basic patterns, and these fracture-initiation patterns were developed into two fracture geometries: simple fracture with only 2-4 strands and complex fracture network with >4 strands. The main reason for this difference is that the initiation and propagation of hydraulic fracture is controlled by the way of fluid circulation, and the cycle time duration and injection rate each played a different role in hydraulic fracturing. At a low injection rate, the initiation and propagation of hydraulic fractures under the high-frequency cycle (cycle time duration = 10 and 20 s) are mainly controlled by the change of injection pressure. Here, the hydraulic energy mainly acts on the rock near the well. The frequent change of injection pressure promotes the initiation of micro-fractures and forms a complex but short hydraulic fracture network. However, when high injection rate is subjected, too high and too low cycle frequencies (cycle time duration = 5 and 40 s) both tend to form a simple fracture, but the fracture has strong extension ability. With that, the similarity criterion of physical phenomena between the on-site prototype and the experimental model were discussed, and these lab-scale results were translated into the fracturing site of HDR.
查看更多>>摘要：The pulsating hydraulic fracturing (PHF) technology can be employed to improve the shale's permeability more effectively comparing to the conventional fracturing method. To understand the mechanism of flow conductivity under the PHF, we investigated the shale's conductivity capacity using pulsating fracturing test device. The experiments are conducted on the different closure pressures to monitor the shale's flow conductivity in the artificial fracture under the pulsating fracturing stimulation. The results reveal that the fracture surface coin-cidence degree (FSCD) and the flow rate are affected by the closure pressure, as well as there is a good linear correlation between variations of FSCD and flow rate. As the closure pressure increases from 4 MPa to 6 MPa, the flow rate declines by 58.82%. Moreover, a prediction model for the conductivity capacity in shale's single fracture under pulsating hydraulic fracturing is proposed. It can well predict the fracture conductivity capacity when the closure pressure range in 4-10 MPa, which is helpful to evaluate the economic benefits of fracturing.
NSTL
Elsevier