Le Ngoc SonPhan Ngoc TrungMasuda, YoshihiroMurata, Sumihiko...
12页
查看更多>>摘要：The Nam-Su is a major naturally fractured basement reservoir (FBR), offshore Vietnam. To date, simulation models of Nam-Su FBR have failed to give an adequate history match without invoking the presence of large aquifers. In a previous study (Son et al., 2007), the authors investigated several possible alternatives to achieve a satisfactory history match. They modeled porosity reduction by compaction along with the change of aquifer size and produced an improved history match that is consistent with the geological nature of the system. The key to such modeling is reservoir rock compressibility. Estimating the values of rock compressibility from cores is a challenge in FBR's due to the failure of coring from a naturally fractured interval, and thus reliable values are not available. We developed a computer-assisted history matching method to resolve these two problems together and save significant time compared to the manual trial-and-error methods used to adjust these parameters generally used in Vietnam. The methodology developed has been applied successfully to determine rock compaction coefficients and adjust aquifers' sizes of the Nam-Su FBR. Comparisons between our adjusted model and the existing model show considerable improvement between computed and measured values. Simulators can always be adjusted to obtain a history match even with geologically unrealistic values. The approach outlined here is more physically realistic than existing approaches and hence should provide/provides better production and other forecasts.
查看更多>>摘要：Circulation loss is a very common and undesirable non-productive time (NPT) event that happens during the oil and gas well drilling operations. Many loss circulation materials (LCM) have been formulated and implemented in the process of gas and oil wells drilling to minimize or mitigate this problem. In-situ calcite precipitation in effective pores can restrict the movement of the water flow between the grains by forming bridges. In this study, different mixes of Enzyme-induced calcite precipitation (EICP) solution are studied and tested in the laboratory to mitigate lost circulation problem. EICP solution is primarily composed of urea, calcium chloride, magnesium chloride, Xanthan Gum, and urease enzyme. Different concentrations and compositions of reagents were tested. The properties of the created precipitates were examined through different techniques such as X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The combination that produced the highest amount of thermally stable calcite with a minimal amount of aragonite, along with the highest precipitation efficiency was further selected for lost circulation application. A solution containing 1M Urea, 0.9M CaCl2, 0.1M MgCl2, 1 g/L Xanthan Gum, and 3 g/L urease was considered as an optimum combination for an EICP process. Lost circulation experiments were carried out in core flooding experiments on a high permeable Indian Limestone sample at room and elevated temperature conditions with the optimum combination of EICP reagents. The permeability of the samples was measured before and after the treatment. Nuclear Magnetic Resonance (NMR) scan was also run before and after the treatment to determine the pore size redistribution. Results showed that the permeability of the samples was reduced by 99%, NMR results showed that the porosity of the samples was also reduced by 20%.
查看更多>>摘要：We apply a numerical well test model that considers the transient flow in well and the complex displacement mechanisms for the multiphase transient analysis of horizontal wells during CO2-EOR. Aimed to perform a systematic and reliable analysis, we run the model on a high-resolution non-uniform grid to accurately capture the transient flow in the near wellbore region as well as the complex displacement process. In this work, we interpret the pressure response curve in two steps to find the root causes of the particular transient behaviors. First, we identify five typical flow regimes through the traditional pressure transient analysis method for horizontal wells which gives us a basic understanding of the characteristics of the pressure response curve. Second, assisted with the corresponding analysis method, we figure out the durations on the curve that correspond to different component banks. By taking the complex displacement mechanisms into consideration, we find that the component banks have a large influence on the curve and identify the root cause of each unique characteristic. Besides, we conduct a systematic sensitivity analysis with respect to multiple parameters such as miscible condition, wellbore storage coefficient, skin factor, horizontal well length, anisotropy, and amount of injected CO2. Finally, we have a better understanding of the transient pressure behavior of horizontal wells during CO2-EOR, find a way to determine the miscibility underground, and feel more confident in applying the pressure transient data for analysis and parameter estimation.
查看更多>>摘要：The evaluation of pore-throat structure is essential for the exploration and exploitation of tight oil and gas reservoirs. In this study, various experiments such as casting thin section (CTS), scanning electron microscope (SEM), mercury intrusion porosimetry (MIP), and nuclear magnetic resonance (NMR) are used to investigate the pore-throat structure and fractal characteristics of the tight sandstone from the Permian Shihezi Formation in the Sulige area, Ordos Basin. The type and size of tight sandstone pores and throats are qualitatively analyzed by using CTS and SEM. However, the structural parameters such as the size and distribution of tight sandstone pores and throats are quantitatively calculated by HPMI, CRMI, and NMR. According to the advantages and disadvantages of each method, the HPMI and NMR are combined to characterize the full-size pore-throat distribution (PSD) of tight sandstone. Based on the fractal theory, the fractal dimensions (D) of pore-throat of tight sandstone are evaluated by HPMI, CRMI, and NMR. The result shows the pores in the tight sandstone are mainly residual intergranular pores, dissolution pores, and inter-crystalline pores. There are few micro-cracks developed, and the throats are mainly tubular and curved sheets. The full-size PSD curve of tight sandstone presents the characteristics of the bimodal and unimodal distribution. It has a good agreement with petrophysical properties and movable fluid saturation. Different experimental methods can get different D. HPMI and NMR have different detection ranges and diverse principles for pore-throat evaluation, making sandstone's diverse fractal characteristics. The CRMI is more representative for studying the fractal characteristics of the throat. Moreover, there are two different types of throats: large throat and small throat. These throats have a double fractal feature. The relationship between D and the physical properties analyzes the parameters of the pore-throat structure, suggesting larger the D, the worse the physical properties of the reservoir. The development of the throat (especially the larger throat) controls the storage and fluid flow-ability of tight sandstone reservoirs. Mercury saturation, movable fluid saturation, and D are negatively correlated, indicating that the complicated pore-throat structure will reduce permeability and destroy the free fluid storage space.
查看更多>>摘要：Shut-in after hydraulic fracturing can make full use of fracturing fluid imbibition and improve well productivity. However, how to determine a scientific shut-in time is an important problem for reservoir engineers. Therefore, an efficient model was proposed in this paper to fill this gap and then applied in the shale oil reservoirs. An analytical model of pressure distribution and stimulation reservoir volume was first developed, which includes the process of fracturing fluid injection and well shut in. A good agreement was obtained between the calculated pressure data and field data. Afterward, the imbibition experiments of 15 core samples from shale oil reservoir were carried out and the imbibition equilibrium time was observed. Finally, we calculated the shut-in time by summation of the time of fracturing fluid volume stabilization (stimulation volume stabilization) and imbibition equilibrium time. Results show that pressure diffuses during fracturing fluid injection and the pressure balance during well shut-in both impact the time of fracturing fluid volume stabilization (stimulation volume stabilization). Furthermore, a higher permeability can increase fluid flow capacity and accelerate the time of fracturing fluid volume stabilization. A scientific shut-in time should include pressure balance time and fracturing fluid imbibition equilibrium time. This work can provide a strong basis for optimization the shut-in time and useful insights into fracturing operation in shale oil reservoirs.
Guo, BoyunShaibu, RashidWortman, Philip B.Lee, Jim...
11页
查看更多>>摘要：Production decline from wells producing from shale rocks is typically quite rapid. One possible factor responsible for such decline is loss in fracture conductivity. This is true in the case of the Tuscaloosa Marine shale reservoir. In this work, the stress-dependent fracture conductivity of TMS core samples is investigated using five propped cores under varying stress conditions. In addition, the effects of static rock mechanical properties and rock mineralogy on conductivity decline are investigated. The mineralogy of each core sample was determined by Xray Diffraction analysis. Fracture conductivity was measured using a Hassler-type pressure core holder with a pressure rating of 15,000 psi (103.42 MPa). Estimated rock mechanical properties showed that shale anisotropy could affect fracture conductivity. The time decline in conductivity revealed two possible decline trends, a) decline from the reduction in induced fracture width, and b) decline from the healing of developed micro-cracks. An exponential decline in fracture conductivity with increasing confinement pressure was observed with an average decline rate constant of 3.15 x 10- 10 mPaxfffd; 1. While rock mineralogy did not have any clear relationship with conductivity decline, the effects of rock mechanical properties were only important at 10.34 MPa confinement pressure and above. The observation showed that a high Young's modulus correlate to high conductivity, whereas a high Poisson's ratio correlate to low conductivity. This study provides useful observations for optimizing fracture design to enhance well productivity in the TMS.
查看更多>>摘要：During drilling operations, the drill bit is worn out while breaking the rock. The roller bit is an important rockbreaking tool, but our research on its wear mechanism is still inadequate. Therefore, in response to this problem, this paper establishes a fractal characterization method for surface roughness based on the morphological features of the rock and bit surface. Combining the worn bit surface morphology and energy spectrum analysis results, it is determined that the wear mechanism of roller bit teeth is mainly abrasive wear, fatigue wear and adhesive wear, which are mainly squeezing and spalling. The rock is broken by roller bit under the action of drilling pressure and tangential force, so the contact force model of the single tooth pressed into the rock is established, and the reacting force of the rock on the bit tooth is deduced based on the rock crush conditions. According to the rolling friction characteristics of roller cone bits, the friction coefficient in rolling conditions is calculated. Then, according to the wear mechanism of the cone bit, the actual contact force and real contact area between the cone bit and rock at the bottom of the hole, a roller bit teeth wear equation is established, consisting of rock properties, bit properties and working condition parameters. The bit parameters and drilling parameters are regarded as controllable parameters, and the rock properties are regarded as uncontrollable parameters. In order to highlight the basic parameters of rock, the controllable parameters in the equation are standardized. The calculated wear degree can better reflect the wear ability of rock to drill bit. This result is of great significance for the factor prediction of formation abrasiveness and bit selection.
查看更多>>摘要：Lithofacies identification in carbonate reservoirs using conventional well logs is a typically complex nonlinear problem due to influences of multiple factors, such as fluids and fractures. Kernel Fisher discriminant analysis (KFD) is a useful nonlinear single-kernelled method to classify lithofacies. However, the prediction capacity of a single kernel is limited to some extent, especially for complicated lithofacies identification problems. To alleviate this issue, a multiple kernel Fisher discriminant analysis (MKFD) method, an improved KFD, is introduced in this work. MKFD utilizes multi-scaled kernel functions to realize the optimal nonlinear mapping instead of a single kernel used by KFD, which can extract more efficient nonlinear lithologic features. It first increases dimension of input data to obtain more nonlinear features and then reduces dimension to extract effective information from these features for lithofacies identification. To examine the effectiveness of MKFD for lithofacies identification in carbonate reservoirs, a conventional log dataset labelled by rock cores from carbonate reservoirs of Asmari Formation in Paleogene Oligocene-Neogene Miocene in A Oilfield, Zagros Basin, Iraq is used. Both statistical (confusion matrix) and geological evaluations (blind well test) indicate that MKFD outperforms KFD and the prediction results of MKFD are more consistent with rock cores. It has been demonstrated that MKFD can provide an accurate and effective means for lithofacies identification in carbonate reservoirs.
查看更多>>摘要：The accurate prediction of sandstone permeability from variables such as porosity, composition, and texture is one of the major problems in petroleum geology. However, the application of geological variables related to diagenesis in permeability prediction models is relatively rare, especially the anomalous variations of clay content and type. This study investigates the differential control of sedimentation and diagenesis on permeability using a comprehensive analysis of cores, thin sections, routine core analysis, X-ray diffraction, and scanning electron microscopy from sandstone samples in the third member of the Weizhou Formation (Ew(3)), Weizhou 12-X oilfield, Weixinan Sag, Beibu Gulf Basin, China. An innovative sandstone reservoir permeability prediction model is proposed by introducing the clay factor beta confining the effect of clay minerals on permeability, predicting the spatial distribution of diagenetic index (I-D) using the Diagenetic Modeling System (DMS), and improving the Walderhaug permeability prediction model. The permeability of the well evaluated in the study was predicted with the relative and absolute errors changing from 0.01 mD to 192.65 mD and from 0.00 to 1.00, with an average values of 38.6 mD and 0.33, respectively, based on the sandstone reservoir permeability prediction model in Ew(3). The permeability predicted by the permeability prediction model matches well with the measured permeability in Ew(3). The results indicate that permeability is successfully predicted by the modified Walderhaug permeability prediction model for most sandstone reservoirs with strong diagenesis (such as anomalous changes in clay mineral types and content) under the background of a single distributary channel sedimentary microfacies. In general, anomalously high permeability zones are preferentially distributed in dominant sedimentary-diagenetic facies.
查看更多>>摘要：The prediction of pipe sticking accidents due to wellbore uncleanness is significant for safe drilling, while existing qualitative prediction methods result in inaccuracy and lateness. To cover the shortages, a novel quantitative pipe sticking prediction method is established to achieve pipe sticking prediction early in drilling preparatory stage. First, the additional axial forces and torques on the drill string exerted by accumulated cuttings are calculated in tripping out, tripping in, back reaming and reaming processes based on granular mechanics. Second, the torque and drag model is modified considering additional axial forces and torques to calculate the hook load and the top drive torque. Finally, the pipe sticking prediction is conducted according to the critical hook load and the critical top drive torque in a specific drilling process. A case study including comparison with the classical model and sensitivity analysis is conducted. Under the given condition, pipe sticking risk is predicted with the new mothed by anticipating hook loads (5524.67 and -667.71 kN) and top drive torques (60.87 and 66.36 kN m) exceeding the critical values. The hook load and the top drive torque change exponentially with the travelling distance. In tripping out and back reaming processes from 4350 to 4250 m, the hook load and the top drive torque respectively increase for 1894.36 kN and 53.99 kN m. In tripping in and reaming processes from 3450 to 3550 m, the hook load decreases for 29925.66 kN and the top drive torque increases for 157.3 kN m. According to the sensitivity analysis, low frictional coefficients, initial cutting volume fractions, torque and drag frictional factors and high junk slot ratios are required to reduce the risk of pipe sticking. This study provides a timely and quantitative prediction method for pipe sticking accidents due to wellbore uncleanness in long horizontal drilling.
NSTL
Elsevier