查看更多>>摘要：Hydraulic conductivity of natural shear fractures is considered with regard to the current stress state of fractured rocks. The paper focuses on spatial orientations of hydraulically conductive shear fractures existing in naturally fractured fluid saturated rocks. The concept of critically stressed fractures is used for the analysis. The paper presents an algorithm and analytical solution that can be used to obtain all possible spatial orientations of critically stressed fractures for an arbitrary stress tensor. The proposed solution is explicit, providing functionality to predict the spatial orientations of hydraulically conductive fractures for rocks subjected to arbitrary stresses. The results obtained from the presented methodology can be directly used to deal with results of geomechanical modeling of naturally fractured reservoirs development. Several analyses of applying the obtained solution in practice are presented in the paper: spatial orientations of critically stressed fractures are obtained for cases of different gradual changes in stress tensor components under specific conditions, providing an understanding of the main tendencies in these spatial orientations. According to the obtained results, spatial orientations of critically stressed fractures tend to be related to directions of principal stresses, while magnitudes of principal stresses govern the shapes of zones containing poles to critically stressed fractures at stereonets. The influence of the following major geomechanical factors standing for hydraulic conductivity of natural fractures is studied: magnitudes and directions of principal stresses, friction coefficient of rock. Stereonets are used to visualize the changes in spatial orientations of hydraulically conductive fractures, caused by alteration of stress state of the rock.
Kassem, Ahmed A.Osman, Osama A.Nabawy, Bassem S.Baghdady, Ashraf R....
25页
查看更多>>摘要：The channelized carbonate reservoirs played important role in the global hydrocarbon production. This study presents a new contribution to the carbonate platform system of the Turonian sediments in the Gulf of Suez. The siliciclastic fluvial channelized system incised the carbonate platform in October Field to deposit excellent reservoir unit. Also, the study interprets the facies change, depositional environment, and petrophysical characteristics of the Turonian Wata sequence, to figure out the fluvial channel reservoir distribution and discrimination using surface outcrops in addition to five cored wells. The petrographic analysis and depositional settings interpretations were conducted to the subsurface and outcrop samples. Then, the conventional core analysis measurements were combined with borehole logs for optimum reservoir discrimination, rock typing, and flow units interpretation. Besides, we studied the reservoir heterogeneity and predict permeability and reservoir rock typing in the un-cored intervals. Our finding revealed that the Wata Formation is subdivided into three main lithological units characterized by 16 microfacies. The lower and upper ones are carbonate dominated, composed of wackestones, packstones, and grainstones which is deposited in platform setting belong to lower/middle shelf and mid/outer shelf to outer ramp setting respectively. The middle unit is classified into lower and upper zones, where the lower clastic zone is composed of vari-sized sandstones, siltstone, and mudstone with some plant remains deposited in a point bar of fluvial channel and flood plains. The upper zone is composed of clastic/ carbonate intercalations deposited in intertidal/shelf settings. The integration between the petrography and petrophysics enables discriminating the Wata sandstone reservoir into four static rock types (PSRT 1-4), which are controlling its reservoir quality and heterogeneity. The PSRT1 and PSRT2 have the best reservoir quality in the channelized unit and are recommended to be tracked along with October Field. The HFU2 and HFU3 are the main flow capacity in the Wata reservoir, composed of PSRT1 and PSRT2, and represented by the calcareous and ferruginous quartz arenite microfacies. This study presented a secondary dolomitized microfacies with 85% oil potentiality resulted from the incision of the fluvial channel above the aerially exposed carbonate lower unit. The research addressed the optimized petrophysical properties and reservoir heterogeneity of the channelized Wata sequences. In addition, it highlights a guidelines for further exploration and production of these reservoirs in the basin.
查看更多>>摘要：Drilling fluid loss in fractured formations is still an engineering problem to be solved. This work establishes an analysis method for fluid loss in fractured formation based on geomechanics modeling. The method is applied in the Bohai B oilfield in Bohai Bay, China. Three-dimensional fracture intensity and lost circulation pressure of the reservoir are established. Meanwhile, the influence of fracture dip angle and fracture width on fluid loss and the performance of onsite lost circulation materials are investigated. The results show that the reservoir of Bohai B oilfield has extensively developed fractures and the safety mud density window is very narrow in the fracture development areas. The areas with fracture development are strongly correlated to the zones of high fluid loss risk. In addition to fracture size, the magnitude of fluid loss is also closely related to the dip angle of the fractures, and a higher fracture dip aggravates fluid loss. The proposed method can effectively characterize the development of fractures, evaluate the impact of fracture characteristics on fluid loss, and identify locations with a high risk of fluid loss.
查看更多>>摘要：New design of system for providing cold air within the building was recommended in this study. Mixture of TiO2 (with fraction of 0.04) and RT25 was applied as NEPCM and three-lobed ducts were filled with them. Air become warmer outside the building owing to sun radiation and with moving along the channel, its temperature reduces because of melting procedure. Homogeneous model for NEPCM has been incorporated in equations of paraffin zone which contain laminar flow. Also, the range of inlet velocity contains the turbulent flow at air flow with Re = 6e3 to 1e4. The temperature of inlet air (T-in) was assumed as another active parameter. Irreversibility of system has been analyzed, too. Testing the exactness of procedure of modeling was applied according to previous published work and good accommodation has been reported. To decline the computing price, size of grid and time step were analyzed to find the optimized values. With adding TiO2 particles, the temperature of paraffin enhances and speeds of charging increases. At t = 5hr, dispersing nano-powders makes temperature and LF to grow around 0.19% and 0.79%, respectively. The required time declines around 31.26% and 40.78% with rise of Re and Tin.
查看更多>>摘要：There are some problems in coiled tubing drilling in deep horizontal wells, such as large buckling friction and difficult extension drilling. At present, a friction reduction tool based on Coanda effect is used to improve the problems existing in coiled tubing drilling. However, there are few systematic studies on the working characteristics of the tool, and the tool power matching is poor. Therefore, based on the basic theory of wall attached jet, the numerical model of friction reducing tool is established. The effects of the working parameters (inlet flow rate, drilling mud density) and the structural parameters (thickness of the flow channel, outlet diameter) on the working characteristics of the tool are analyzed. The results show that, the working pressure drop increases with the increase of working parameters, and decreases with the increase of structural parameters. The cleft tip, vortex chamber and outlet are vulnerable to erosion. The erosion rate is positively correlated with the working characteristics. Among them, the inlet flow rate has the most significant effect on the working performance and erosion rate of the tool. The research results provide a theoretical basis for the field application and parameter selection of friction reduction tools.
查看更多>>摘要：The fatigue damage of subsea wellhead has become one of the important issues in deepwater oil and gas industry. Current research on the fatigue damage evaluation of the subsea wellhead is based on the recommended practices (DNVGL-RP-0142, 2015; DNVGL-RP-E104, 2018), where the influence of the temperature and pressure is ignored. This paper presents the fatigue damage of the subsea wellhead under the condition that the temperature and pressure is considered. Firstly, the analysis model of the temperature and pressure is established. Then, the influence of the temperature and pressure are considered in the local response analysis based on the recommended practices. In addition, the interaction between the conductor and soil is evaluated by the Goodman element model and the P -y model in the local response analysis. Finally, the accumulated fatigue damage of the subsea wellhead is obtained according to the S-N curve recommended by DNVGL (DNVGL-RP-C203 (2016)). On this basis, the influence of the temperature, pressure, top of cement (TOC), contact surface model on the fatigue damage of the subsea wellhead is discussed in detail. Analysis results show that both the temperature and pressure have effect on the fatigue damage of the subsea wellhead. The ranking of the influence strength is temperature and pressure (TP), pressure (P) and temperature(T). The fatigue damage of the subsea wellhead would be underestimated if the temperature or pressure is neglected. This study has guiding significance for fatigue damage evaluation of the subsea wellhead and safe operation of deepwater drilling.
查看更多>>摘要：The accurate estimation of production is the bottleneck technique that constraints the efficient development of oil and gas fields. However, such multivariate and asymmetric reservoir parameters and highly nonlinear fluid flow behavior stake a stringent claim for precise production forecast, which makes semi-analytical modeling and numerical simulation techniques expose challenges. Based on the applications of data modeling methods in the prediction of oil and gas production, this paper proposes the procedures of data-driven models for multivariate oil field data with small samples. In addition, the strengths, weaknesses and limitations of widely used data driven models and their combination models are analyzed in detail, and the experiences and lessons in oil and gas production prediction are summarized based on the applications of data-driven models in oilfield cases. Furthermore, the data modeling method for flow equations with complex boundary and mechanism will be a challenge and future direction to make production predictions more quickly and accurately.
查看更多>>摘要：Superparamagnetic Iron Oxide Nanoparticles (SPION) exhibit relatively low toxicity and cost, while their chemical versatility provides an interesting class of materials for the development of nanofluids for advanced oil recovery. In this article, we present a comprehensive characterization of SPION modified with the disodium 4,5dihydroxy-1,3-benzenedisulfonate (HBS) anionic ligand, forming a coating capable of improving the colloidal stability of the nanofluid, even in brine containing up to 22,000 ppm of sodium chloride. Fourier-transform infrared spectroscopy (FTIR) and x-ray photoelectron spectrometry (XPS) data demonstrated the chemical modification of the surface of the particles by the HBS ligand, through the linking of the catechol group, expose the sulfonate groups on the surface of the SPION-HBS. The anionic groups modify the surface charge distribution of the nanoparticles, shifting the isoelectric point of the nanoparticles from pH 6.3 (SPION) to less than pH 2 (SPION-HBS). This fact affords greater stability, supporting the drastic conditions of enhanced oil recovery (EOR) application. The interfacial properties of these particles were also investigated, revealing a slight reduction in the interfacial tension (IFT) of the nanofluid/oil, and small changes in the contact angle (CA) measured as a decane droplet on a glass surface. Despite the slight reduction in IFT and CA, spontaneous imbibition experiments showed a dramatic improvement in oil production in the nanofluid group, reaching a relative value of 2.75 times greater than in the control, at the end of the 5-month trial. The higher oil production achieved with the SPIONHBS nanofluid can be attributed to a more efficient change in wettability, reflecting the role of electrostatic interactions between the sulfonate groups at the particle surface and the porous surface of limestone rock. Since there was no surfactant in the composition of the nanofluid, the observed effects can only be attributed to the influence of the nanoparticles in the EOR process.
查看更多>>摘要：Natural gas flow in shale pore systems determines the accumulation and production of shale gas. Under the conditions of reservoir, gas flow in such shale pores is significantly different from that in conventional reservoirs. Studies of gas flow under such conditions are usually limited to simple pore models with tube/slit geometries or bundle of tubes/slits, which constructs important theoretical basis, however, cannot represent the pore networks of shales. For directly simulating gas flow in complex media, we proposed a modified microscale lattice Boltzmann (MM-LB) model, in which the local effective mean free path (MFP) at any location of the pore system with complex geometry corrected by a custom two-dimensional (2D) eight-direction wall function was considered to capture the effective relaxation time for each lattice node in LB model. What's more, to consider slip velocity at solid boundaries, a combined bounce-back specular-reflection (BSR) scheme was adopted. The MM-LB model was firstly validated in 2D pore systems with simple slit/channel geometries and complex geometries (square and triangular cylinder flows) and in a 3D Sierpinski carpet, where good agreements with linearized Boltzmann solutions, molecular dynamics (MD) simulation and the direct simulation BGK (DSBGK) method results were found. Using the MM-LB model, we quantified the end effect on gas flow through pore throat and found that the end effect is caused by not only the streaming bending but also the variance of MFP (i.e., viscosity) throughout the pore throat. Finally, we applied this model to simulate shale gas flow in three digital reconstructions of kerogen pore systems and compared the results of apparent permeability prediction with Klinkenberg model and Beskok-Karniadakis (B-K) model. It is showed that the apparent permeability of gas flow in shales decreases with the decrease of temperature or the increase of pressure, and the pressure has a greater effect than temperature. For similar pore structures, the apparent permeability increases with the width of pore body and pore throat, especially the pore throat, which dominates the overall flow velocity of the entire flow field. According to the comparison and analysis of the results of MM-LB model with Klinkenberg and B-K model, it can be inferred that permeability prediction based on models of tube/slit (or bundle of tube/slit) pores misestimate the apparent permeability due to ignoring the connectivity and the end effect, especially for the conditions of lower pressures and nanoscale pore spaces.
查看更多>>摘要：With the widely use of hydraulic fracturing technique, large volumes of fracturing fluids are injected into shale reservoirs. The physical and chemical reactions between fracturing fluids and shale will change the surface roughness of shale fractures, which further impacts the production efficiency of hydrocarbons. To quantify the impacts of fracturing fluids on shale fracture roughness, a series of imbibition tests were conducted on shale samples soaked in different fracturing fluids (acid (pH = 6), neutral (pH = 7) and alkaline (pH = 8)) with different time (short-term (0-3 months) and long-term (3-12 months)). The surface morphology, microstructure, mineral composition, and element changes of shale samples before and after imbibition were determined. The results showed that: (1) pyrite and kaolinite were the main minerals that dissolved in the short-term of imbibition. The dissolution of pyrite caused the rapid decreasing of pH values for all fracturing fluids (decreased by 43%-51%). In the long-term of imbibition, clay minerals (illite-montmorillonite) and feldspar were the major dissolved minerals, resulting in the rise of pH values (increased by 10%-19%). (2) the dissolution, hydrolysis, and hydration process during imbibition resulted in the increase of fractal dimension (increased by 9%-30%). Alkaline fracturing fluid had higher effect on the roughness of shale than that of acid and neutral fracturing fluids. (3) the joint homogeneity on the shale fracture surface which obtained from the joint rose diagram revealed that acidic and neutral fracturing fluids enhanced the joint homogeneity (increased by 64% and 74.6%), whereas alkaline fracturing fluid weakened the joint homogeneity, which decreased by 43.8%. In this study, the impact of fluid-rock interaction on shale fracture surface roughness is explored for the first time, a variety of methods are used to evaluate, and the differences of different methods are compared. The results show that different pH fracturing fluids have significant changes in the surface roughness of shale fractures. For shale formation with high pyrite content, alkaline fracturing fluid has stronger reconstruction ability. Above conclusions may have significant impact on the efficiency of hydraulic fracturing.
NSTL
Elsevier