Maior, Caio B. S.Macedo, July B.Lins, Isis D.Moura, Marcio C....
10页
查看更多>>摘要：Reliability estimation is an essential task to ensure predictability on the life of equipment installed in oil wells, allowing forecasting costs, planning maintenance, and estimating system availability. However, data may be rather scarce and/or expensive to obtain, especially for technologies under development in the Oil and Gas (O&G) industry. The information is frequently available in generic databases and expert opinions. In the Bayesian framework, the prior knowledge about a system's reliability is updated as a new field and/or test data are gathered. This paper proposes an approach that does not require direct elicitation of parameters to define informative prior distributions for the reliability function using fault tree analysis, expert's opinions, and/or generic data at the system level of equipment under development. Specifically, the method-of-moments and maximum-entropy are adopted to propagate downward the uncertainty from the system level through the failure modes until the basic events of the fault tree, weighted by the expert knowledge of the failure behavior. Then, in possession of all prior distributions of the basic events, the information may be propagated upward based on Monte Carlo simulation to update the system reliability distribution. Finally, we present a case study of the proposed methodology applied to a novel open-hole expandable packer, a completion equipment recently installed in a Brazilian oil field. The failure modes and failure causes are discussed, and, after expert elicitation, the definition of the informative prior distribution is achieved. Therefore, we estimate the reliability for a given time and assess if the novel equipment attains the company's risk target, taking O&G standards as reference.
查看更多>>摘要：The nuclear magnetic resonance (NMR) technique is a crucial means for formation evaluation. It can provide an accurate set of formation parameters in single-phase-flow reservoirs, such as porosity, permeability, and pore structure distribution; however, in most cases, there are hydrocarbon-water two-phase fluids in the reservoirs. The secondary change of the T2 distribution makes the accuracy of the evaluation a challenge. Hence, it is necessary to clarify the impact of changes in hydrocarbon content on the response of NMR signals before using the traditional evaluation methods. In this paper, we analyzed the response mechanism of NMR T2 distribution under different saturation conditions. Based on the theoretical derivation, we established a nuclear magnetic model that describes the relation among the T2 geometric mean value of water signal, hydrocarbon signal, and water saturation. The accuracy of each model part was verified by numerical simulation. In addition, the calculation results in core samples show that the proposed model is more effective and reliable than two existing models (the T2 saturation ratio model and the Xiao empirical model), especially in extreme conditions (irreducible water and hydrocarbon saturated samples). Finally, we applied the proposed model to field application in the Tertiary formation in the Bohai Bay Basin, China, which achieved good effects in the NMR fluid substitution and the NMR saturation evaluation.
Shahmohammadi, BorhanChahardowli, MohammadSimjoo, Mohammad
14页
查看更多>>摘要：This study aims to provide new insights into the interactions among an acidic crude-oil, brine with different salinities and clay using flow experiments in montmorillonite-coated micromodels. To this end, a series of oildisplacement experiments are performed in a transparent clay - coated micromodel. In addition, salinityscreening tests, pH and IFT measurements are performed to support the results of flow-experiments. It is shown that during water injection into a clay-coated micromodel, polar components of crude oil partition between oil/water phases and form an emulsified phase. With the 90% reduction in water salinity, the partitioning of crude oil polar components in the aqueous phase is increased. Such partitioning lead to a significant reduction in the pH of the aqueous phase. This observation is supported by an increase in the IFT of oil/brine due to the decrease of crude oil polar components. Salinity screening tests show that there is a critical water salinity, i.e., below the critical point, a large amount of crude oil polar components is partitioned between phases, which can be attributed to the polarization effect. Overall, results show that low salinity water injection benefits from formation of an emulsified phase and wettability alteration to improve oil recovery in the microscale.
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%.
Cartagena-Perez, D. F.Alzate-Espinosa, G. A.Arbelaez-Londono, A.
9页
查看更多>>摘要：This paper focuses on understanding the conceptual evolution and practice of sand management through six stages. The geomechanical mechanisms leading to sand production are presented at different scales for comprehensive conceptualization. The concept of "conservatism" is assumed when analyzing passive and active methods for sand control and in the models and approaches to the sanding risk. There is a strong relationship between oil prices and publications (papers) about sand management and sand control. At its core, sand management considers sand production not as a problem but as a phenomenon that demands an intensive study of the genesis and mechanism of sanding. However, the risk assessment must be considered instead of avoiding sand influx as sand control currently does. This paper illustrates how the focus of technical literature and practices has adjusted its questions about sand management through different stages of understanding. Therefore, this paper helps the technical community understand sand management from its historical conceptualization and its relationship with multiple external factors.
查看更多>>摘要：Organic-rich terrestrial shales, the most promising shale oil production layer, are widely distributed in major basins in China, and they are usually interbedded salt rocks. Understanding the role of salt rocks in the organic matter (OM) enrichment in shale sediments has important enlightenment for shale oil exploration. The shale of the third member of the Eocene Shahejie Formation (Es-3 shales) in the Dongpu depression of the Bohai Bay Basin is dominated by clay minerals, with a non-negligible proportion of gypsum, anhydrite, and halite. They contain abundant OM with a mean total organic carbon content of 1.26 wt %. The development of salt rocks revealed the arid and transiently humid climate during the Es-3 period and an evaporating environment with a shallow lake level at the Dongpu Ancient Lake Basin. OM enrichment was synthetically affected by the palaeoenvironment during the Es-3 period. The paleolake with a paleosalinity as high as 23.43 parts per thousand was nutritious and promoted the prosperity of salt loving organisms causing high paleoproductivity. The Es-3 shales were deposited under anoxic and dysoxic conditions in a deep lake, which provided good conditions for OM preservation. In addition, salt rocks itself are good caprocks to prevent the loss of shale oil. Under the dual guarantee of high productivity and good preservation conditions, OM is much enriched in the Es-3 shales. OM enrichment was synthetically affected by the palaeoenvironment during the Es-3 period. The horizontal difference of paleoclimate controlled the discrepancy of salinastones distribution, OM enrichment, paleosalinity, andpaleoproductivity in different saline surroundings of Dongpu Depression. The composite patterns of palaeoenvironmental variation affected the vertical anisotropic enrichment of OM. Seven stages were divided for the Es-3 period to reflect the effects of vertical anisotropy on OM enrichment. Stages I, V, and, VII deposited thick salt under an arid climate and provided a good seal-capping and preservation condition for the OM enriched in stages II, III, IV, and VI. The shale reservoirs deposited in stages III and IV were favorable for shale oil exploration.
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：A viscoelastic surfactant (VES) fluid blends with CO2 to form the foam fracturing fluid. To obtain the dynamic proppant-carrying behaviors of the VES-CO2 foam fluid, an experimental system with a horizontal transparent tube and a visual fracture is built. In the horizontal pipeline, it is displayed that the critical settling flow velocity of the ceramsite proppant in the flowing VES-CO2 foam fluid increases with the temperature. Further, the critical settling flow velocity initially decreases and then increases with both the increases of the foam quality and the proppant ratio, and its transition points are at the foam quality of 0.75-0.80 and at the proppant ratio of 0.25, respectively. In addition, considering the influencing parameters in the experiments, we obtain a correlation equation of the critical settling flow velocity. In the experiments of the fracture observation section, the height of the equilibrium sand bank and the angle of repose are mainly investigated. Both of these two parameters decrease as the foam quality, as well as the injection flow velocity, is increased. Especially, it is found that the angle of repose is below 20 degrees at larger injection flow velocity.
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.
NSTL
Elsevier