The purpose of this study was to discuss shape, scale and superimposed types of sandy gravel bodies in sandy-gravel braided distributary channel. Lithofacies analysis, hierarchy bounding surface analysis and subsurface dense well pattern combining with outcrops method were used to examine reservoir architecture patterns of sandy gravel braided distributary channel based on cores, well logging, and outcrops data, and the reservoir architecture patterns of sandy gravel braided distributary channels in different grades have been established. The study shows: (1) The main reservoir architecture elements for sandy gravel braided channel delta are distributary channel and overbank sand, while reservoir flow barrier elements are interchannel and lacustrine mudstone. (2) The compound sand bodies in the sandy gravel braided delta distributary channel take on three shapes: sheet-like distributary channel sand body, interweave strip distributary channel sand body, single strip distributary channel sand body. (3) Identification marks of single distributary channel include: elevation of sand body top, lateral overlaying, “thick-thin-thick” feature of sand bodies, interchannel mudstone and overbank sand between distributary channels and the differences in well log curve shape of sand bodies. (4) Nine lithofacies types were distinguished in distributary channel unit interior, different channel units have different lithofacies association sequence.
This paper focuses on the Longwangmiao gas reservoir in Moxi-Gaoshiti area, Sichuan Basin. Starting from the tectonic evolution perspective, though comparing biological marker compound and analyzing fluid inclusions, the oil & gas origin and accumulation evolution of Longwangmiao Formation are systematic studied with reference to the burial-thermal evolution of single well geological history in the study area. It is suggested that the oil & gas reservoir is generally characterized by early accumulation, multi-stage filling, late cracking and later adjustment. The oil and gas were mainly sourced from lower Cambrian Qiongzhusi Formation, partly from the Permian source rock. During the geological period, 3 major oil & gas fillings occurred in the Longwangmiao Formation, namely Caledonian-Hercynian filling that was small in scale and produced the first phase of paleo-oil reservoir that soon destroyed by Caledonian movement uplift, large-scale Permian filling that gave rise to the second-phase of paleo-oil reservoir and the Triassic-Jurassic filling that enriched the second phase of paleo-oil reservoir. Finally, the paleo-oil reservoir experienced an in-situ cracking during the cretaceous period that gave rise to a natural gas reservoir and left behind carbonaceous bitumen and oily bitumen in the holes of the Longwangmiao Formation.
The development of shale reservoirs has brought a paradigm shift in the worldwide energy equation. This entails developing robust techniques to properly evaluate and unlock the potential of those reservoirs. The application of Nuclear Magnetic Resonance techniques in fluid typing and properties estimation is well-developed in conventional reservoirs. However, Shale reservoirs characteristics like pore size, organic matter, clay content, wettability, adsorption, and mineralogy would limit the applicability of the used interpretation methods and correlation. Some of these limitations include the inapplicability of the controlling equations that were derived assuming fast relaxation regime, the overlap of different fluids peaks and the lack of robust correlation to estimate fluid properties in shale. This study presents a state-of-the-art review of the main contributions presented on fluid typing methods and correlations in both experimental and theoretical side. The study involves Dual Tw, Dual Te, and doping agent's application, T1-T2, D-T2 and T2sec vs. T1/T2 methods. In addition, fluid properties estimation such as density, viscosity and the gas-oil ratio is discussed. This study investigates the applicability of these methods along with a study of the current fluid properties correlations and their limitations. Moreover, it recommends the appropriate method and correlation which are capable of tackling shale heterogeneity.
Thousands of horizontal wells are drilled into the shale formations across the U.S. and hydrocarbon production is substantially increased during past years. This fact is accredited to advances obtained in hydraulic fracturing and pad drilling technologies. The contribution of shale rock surface desorption to production is widely accepted and confirmed by laboratory and field evidences. Nevertheless, the subsequent changes in porosity and permeability due to desorption combined with hydraulic fracture closures caused by increased net effective rock stress state, have not been captured in current shale modeling and simulation. Hence, it is essential to investigate the effects of induced permeability, porosity, and stress by desorption on ultimate hydrocarbon recovery.
We have developed a numerical model to study the effect of changes in porosity, permeability and compaction on four major U.S. shale formations considering their Langmuir isotherm desorption behavior. These resources include; Marcellus, New Albany, Barnett and Haynesville Shales. First, we introduced a model that is a physical transport of single-phase gas flow in shale porous rock. Later, the governing equations are implemented into a one-dimensional numerical model and solved using a fully implicit solution method. It is found that the natural gas production is substantially affected by desorption-induced porosity/permeability changes and geomechancis. This paper provides valuable insights into accurate modeling of unconventional reservoirs that is more significant when an even small correction to the future production prediction can enormously contribute to the U.S. economy.
Gas condensate is one of the most different fluids in reservoir simulation due to retrograde condensation in case of pressure reduction. In this kind of fluids, two phenomena named negative inertia and positive coupling, become significant in the high velocity zone around the wellbore. In this study, a modified black oil simulator is developed that take into account the velocity dependent relative permeability. Against the industrial simulator that assumes linear variation of transmissibilities by pressure, modified black oil nonlinear equations are solved directly without linearization. The developed code is validated by ECLIPSE simulator. The behavior of two real gas condensate fluids, a lean and a rich one, are compared with each other. For each fluid, simulations of PVT experiments are carried out to calculate black oil property applying Coats approach for gas condensate fluids. For both fluids, the proposed models for gas condensate velocity dependent relative permeability show different influence of velocity on relative permeability in the same conditions. Moreover, it is observed that higher flow rate of gas production leads to more condensate production during constant rate well testing.
Water saturation determination in core laboratory is known as a cost and time consuming labor. Hitherto, many scientists attempted to estimate accurately water saturation from well-logging data which has a continuous record without losing information. Therefore, various model were introduced to relate reservoir properties and water saturation. Since carbonate reservoir is very heterogeneous in shape and size of pore throat, the relation between water saturation and other carbonates reservoir properties is very complex, and causes considerable overall errors in water saturation calculation. By increasing the usage and improvement of soft computing methods in engineering problems, petroleum engineers have been attended them to measure the petrophysical properties of the reservoir.
In this study, a radial basis function neural network (RBFNN) improved by genetic algorithm has been employed to estimate formation water saturation by using conventional well-logging data. The used logging and core data have been gathered from a carbonated formation from one of oilfield located in south-west Iran, and finally their results of the proposed model were compared with the core analysis results. By checking the testing data from another well, it showed this method had a 0.027 for mean square errors and its correlation coefficient is equal to 0.870. These results implied on high accuracy of this model for oil saturation degree estimation. While the common methods like Archie, had a 0.041 mean square error and 0.720 of the correlation coefficient, which indicate a high ability of RBF model than the other usual empirical methods.
The shale gas reservoirs are composed of porous media of different length scales such as nanopores, micropores, natural fractures and hydraulic fractures, which lead to high heterogeneity. Gas flow from pores to fractures is under different flow regimes and in the control of various flow mechanisms. The gas slippage would have significant effects on gas flow in shale. To obtain the effect of slippage on gas flow in matrix and fractures, contrast experiments were run by using cores with penetration fractures and no fractures from Marine Shale in Southern China under constant confining pressure. The results showed that slippage effect dominates and increases the gas permeability of cores without fractures. To cores with penetration fractures, slippage effect is associated with the closure degree of fractures. Slippage dominates when fractures close under low pore pressure. Slippage weakens due to the fractures opening under high pore pressure. Fracture opening reduces the seepage resistance and slippage effect. The Forchheimer effect occurs and leads to a permeability reduction.
Applying chemical flooding in petroleum reservoirs turns into interesting subject of the recent researches. Developing strategies of the aforementioned method are more robust and precise when they consider both economical point of views (net present value (NPV)) and technical point of views (recovery factor (RF)). In the present study huge attempts are made to propose predictive model for specifying efficiency of chemical flooding in oil reservoirs. To gain this goal, the new type of support vector machine method which evolved by Suykens and Vandewalle was employed. Also, high precise chemical flooding data banks reported in previous works were employed to test and validate the proposed vector machine model. According to the mean square error (MSE), correlation coefficient and average absolute relative deviation, the suggested LSSVM model has acceptable reliability; integrity and robustness. Thus, the proposed intelligent based model can be considered as an alternative model to monitor the efficiency of chemical flooding in oil reservoir when the required experimental data are not available or accessible.
Calculating the absolute open flow potential timely and investigating production capacity so as to adjust working system of production wells is one of main means to effectively recovery gas reservoirs during intermediate and late development stage. In order to obtain the open flow potential of gas wells accurately, a new method which utilized a single steady point was proposed in this research, which was based on deliverability formula of a gas well in pseudo-steady state flow with pseudo-pressure form. The influence on factor B in binomial productivity equation caused by the changed permeability was taken into consideration. According to the stable production data, reservoir permeability K can be determined by iterative method firstly, and the coefficient A, B in binomial productivity equation can be calculated with the open flow potential subsequently. It illustrated clearly by a practical example that the new method was suitable for gas wells especially when the producing pressure drop is large. Additionally, the error between the open flow potential value and interpretation result from the multi-point test was small, which proved it to be more simple, economic and effective than the common one.
Nanoparticles have been widely used to reduce wellbore instability problems of shale formation. In this paper, nanoparticle-containing water-based drilling fluids (WBDFs) and oil-based drilling fluids (OBDFs) were evaluated by running three new tests including spontaneous imbibition, swelling rate and acoustic transit time. Results showed that, for the WBDFs, nanoparticles leaded to higher plastic viscosity (PV) and yield point (YP), and lower API-filtration. Moreover, because pore throats of shale can be plugged by nanoparticles, imbibition amount, swelling rate, and Young's-modulus reduction of shale decreased significantly. Higher concentration of nanoparticles can induce better plugging effect. However, for the OBDFs, nanoparticles did not show these positive effects like the nano WBDFs, even leaded to some negative effects such as higher filtration and larger Young's-modulus reduction. The main reasons are that the silica nanoparticles can easily disperse in the WBDFs, and effectively prevent the filtrate invading into shale by plugging pore throats. But the same silica nanoparticles are difficult to disperse in OBDFs, and do not perform the expected functions. This study indicates that nano WBDFs have great potential to reduce the wellbore instability problems of shale formation.
Acidizing treatment in petroleum reservoirs is a short-term and viable strategy to preserve the productivity of a well. There is a major concern for the degradation of cement sheath integrity, leading to poor zonal isolation and environmental issues. Therefore, it is essential to understand how the cement behaves when attacked by hydrochloric acid. In this study, a cement slurry by incorporation of the Henna extract, as an environmentally friendly cement additive, was synthesized as a potential solution to solve this problem. The characteristics of the treated cement slurry were compared with a reference slurry (w/c = 0.44) which is composed of only cement and water. A kinetic study was carried out to evaluate the adsorption behavior of the cement slurries exposed to an acid solution with 0.1 M HCl in a range of 25 to 55 °C conditions. The features of the cement slurries were evaluated by multiple analytical techniques such as XRD, FTIR, TG, and DSC analysis. From the experimental data, it is concluded that the second-order Lagergren kinetic model revealed to be the best in describing kinetic isotherms taken, because the margin between experimental and calculated values was minor for this model. The results of the characterization and HCl interaction kinetic studies underlined the prominent protective role of Henna extract-modified cement slurry in the enhancement of the cement resistance against acid attack and utilization in environmentally favorable oil well acidizing treatments.
Fang contact model is introduced to analyze stress of the spherical fixed ring journal bearing. Developed calculation programs in the MATLAB software which are utilized to calculate the contact characteristics of roller cone drill bits spherical fixed ring journal bearing. In addition, effects of external load, radius clearance values, and material parameter on the mechanics performance were investigated. The results show that the value of external load has a direct pronounced effect on the contact characteristics of journal bearing. There is a significant positive correlation between contact pressure and external load, radius clearance value, and the Young's modulus of material. However, there is an evident negative correlation between contact radius of journal bearing and radius clearance value, and the Young's modulus of material. The smaller radius clearance value of journal bearing is, the more centralized contact region will be, so the corresponding contact pressure will be higher. From the perspective of reducing friction and wear, we need select the materials which have high strength and good toughness. Not only might this can improve the wear resistance, it also effectively decreases the contact pressure. In this case, we can prolong the service life of roller cone drill bits journal bearing.