Recently, super gas wet and gas wet surfaces have been extensively attended in petroleum industry, as supported by the increasing number of publications in the last decade related to wettability alteration in gas condensate reservoirs. In many cases, contact angle measurement has been employed to assess the wettability alteration. Even though contact angle measurement seems to be a straightforward approach, there exist many misuses of this technique and consequently misinterpretation of the corresponding results. In this regard, a critical inspection of the most recent updated concepts and the intervening parameters in the contact angle based wettability evaluation of liquid-solid-gas systems could aid to provide some remediation to alleviate this problem. To this end, this work presents a survey on the accurate terms and rigorous protocols based on the community of surface science and chemistry. As a preliminary step, advancing, receding, static, and the most stable contact angle terminology are defined. The study is followed by the definition of the contact angle hysteresis effect. The application of surface free energy in the selection of the best gas wet agent is then analyzed. Afterward, the impact of the size-dependent behavior of drop on contact angle is discussed. Finally, a sessile drop experiment is explained to achieve the defined parameters. For future contributions to petroleum industry journals, like this journal, this work could offer an easy use of the conceptual framework for analyzing the results and comparative evaluations in chemical wettability modifier agents.

Imperfect determination of petroleum system processes coincidence, entrapment and charge timing, along with reservoir heterogeneity can considerably cause high risks throughout exploration and development phases of petroleum. Therefore, a complete subsurface visualization of the petroleum system nature, elements and processes, is badly required. To this end, we corroborated, in this study, static reservoir modeling with petroleum system analysis workflows, to better characterize the Cenomanian fluvio-marine reservoir, sandstones of Bahariya Formation, at Bed-2 Field, Abu Gharadig Basin (Western Desert, Egypt). We used dataset of 2D seismic profiles and well logs of eight wells. The geometry and property of the reservoir were acquired performing static reservoir geocellular modeling approach. The geohistory, timing of charge, migration pathways, and accumulation sites were identified performing 1D and 2D basin modeling approaches. Combining both approaches was aimed at identifying new petroleum prospect areas, and estimating the hydrocarbon volumes, that are the need for such poorly-defined petroleum systems area. As indicated by the constructed, robust, reservoir and 1D-2D basin models, an additional hydrocarbon prospect, to the north central part of Bed-2 Field, is proposed to be drilled during the further oilfield development phases of the area. This prospect has all features that adequately lead to reliable inferences regarding the ultimate petroleum potential of the area.

During the drilling process for oil and gas production, a larger number of drilling fluids invade the formation, causing severe formation damage and wellbore collapsing, which seriously hinders the efficient production of deep oil and gas. Although several plugging agents have been developed for efficient fracture sealing in recent years, the development of high-performance plugging agents with self-adaptive ability and high-temperature resistance remain a challenge. Herein, we report the synthesis of an internal rigid and external flexible plugging agent PANS by reversed-phase emulsion polymerization with nano-silica as the rigid core and poly (acrylamide-co-N-vinylpyrrolidone) as a flexible shell. The plugging agent has a median particle size of 10.5 μm and can self-adapt to seal the microfractures and fractures in the formation, leading to an effective reduction in the filtration loss of bentonite water-based drilling fluid under both low temperature and low pressure (LTLP) and high temperature and high pressure (HTHP) conditions. In addition, compared with the neat nano-silica (500 nm), the sealing efficiency of PANS toward 100-120 mesh sand bed was increased by 71.4% after hot rolling at 180°C.

The conglomerate rock is usually featured by strong heterogeneity, high abrasiveness, and poor drillability due to its complex composition and texture, which brought a huge challenge for drilling efficiency. In order to guide the drill bit selection and high-efficiency drilling, the physical, mechanical, and drillability characteristics were investigated for conglomerate rock that collected from the lower Jurassic Ziliujing formation in the Western Sichuan Basin of China. The mineral composition, SEM micro-structure, P-and S-wave velocities, uniaxial and triaxial compressive testing, drillability, abrasiveness were systematically tested and analyzed. The mechanical properties and anti-drilling ability of Ziliujing formation were proposed for a typical deep well of S-07, and the distribution characteristics were analyzed. The results indicated that the Ziliujing rock is rich-in quartz and clay minerals, due to the co-existing of strong quartz gravel and weak argillaceous cement, the Ziliujing rock shows strong heterogeneity. The relationships are roughly linear among UCS, drillability, and grinding weight loss with P-wave velocity. The Young's modulus, UCS, internal friction angle, drillability, and abrasiveness meet the Weibull distribution pattern, while only the Poisson's ratio meets the Kernel Smooth distribution pattern. Logging interpretation results reval that the Ziliujing formation has the Young's modulus of 38.61 ± 17.08 GPa, the Poisson's ratio of 0.327 ± 0.006, the internal friction angle of 49.21 ± 11.00°, the drillability of 8.04 ± 1.54, and the abrasiveness grade of 4.32 ± 1.94. The mechanical properties and anti-drilling ability of logging interpretation are in good agreement with the experimental data. The Ziliujing formation is a kind of hard rock with strong heterogeneity, high strength, poor drillability, and medium abrasiveness. Based on the characteristics of Ziliujing formations, the SV516TAUL PDC bit with non-planar cutters was selected for the field application due to the good abrasion resistance, impact resistance, self-sharpening and thermal stability of the non-planar cutters. The field application shows that the average ROP of the new type drill bit in Ziliujing formation is 2.93 m/h, and the average footage is 225.9 m. Comparing with the traditional PDC bit, the ROP of the new drill bit with non-planar cutters has increased by 67.4%, and the footage has increased by 92.1%. The results of this paper can be utilized to guide the drill bit selection and high-efficiency drilling in conglomerate formation.

In petroleum domain, optimizing hydrocarbon production is essential because it does not only ensure the economic prospects of the petroleum companies, but also fulfills the increasing global demand of energy. However, applying numerical reservoir simulation (NRS) to optimize production can induce high computational footprint. Proxy models are suggested to alleviate this challenge because they are computationally less demanding and able to yield reasonably accurate results. In this paper, we demonstrated how a machine learning technique, namely long short-term memory (LSTM), was applied to develop proxies of a 3D reservoir model. Sampling techniques were employed to create numerous simulation cases which served as the training database to establish the proxies. Upon blind validating the trained proxies, we coupled these proxies with particle swarm optimization to conduct production optimization. Both training and blind validation results illustrated that the proxies had been excellently developed with coefficient of determination, R² of 0.99. We also compared the optimization results produced by NRS and the proxies. The comparison recorded a good level of accuracy that was within 3% error. The proxies were also computationally 3 times faster than NRS. Hence, the proxies have served their practical purposes in this study.

Interwell connectivity is an essential parameter for managing waterflooding operations in a field. Analysis of the tracer injection operation is a well-known approach to studying injected fluids distribution in a reservoir and toward producer wells. Developed in the early 2000s, capacitance-resistance model (CRM) is an analytical approach for waterflooding modeling and optimization. Production/injection data are used as input to model the mass balance and estimate parameters such as the interwell connectivity. In this work, we investigated the accuracy of applying the capacitance-resistance model to mimic a tracer test. Such an approach helps assess the connection between the wells and decide on further field development steps cheaper and quicker. Connectivity values estimated by tracer tests and CRM were analyzed and compared for synthetic and real fields. CRM was capable of modeling waterflooding and estimating production in both fields with acceptable accuracy. Parameters such as well spacing and fluid loss during the injection were considered to improve the accuracy of the CRM approach to calculate the interwell connectivity between injector/producer pairs. Our study showed that CRM could serve as a tool for a quick approximate estimation of interwell connectivity under certain assumptions and is recommended as a replacement for tracer flooding analysis, where the tracer test is not possible or is expensive.

To further understand the characteristics of clay and sand production (hereafter collectively referred to as sand production) and to provide optimization designs of sand control schemes are critical for gas production from clayey silt natural gas hydrate reservoirs in the South China Sea. Thus, gas-water-sand production behavoirs and coupling reservoir subsidence characteristics before, during, and after hydrate dissociation of the clayey silt hydrate reservoirs with different clay contents (5%, 10%, 15%, 20%, 25%, and 30%) have been studied through a self-developed experimental system. The results show that with the increase of clay content, the total mass of sand production first increases and then decreases, and it reaches maximum when the clayey content is 20%. The sand production is the lowest before hydrate dissociation and increases significantly during hydrate dissociation, which mainly occurs in the high-speed gas and water production stage at the beginning of hydrate dissociation. After hydrate dissociation, the sand production decreases significantly. During the whole depressurization process, the clay and free sand particles generally move to the sand outlet due to the fluid driving force and overlying stress extrusion. However, for conditions of high clay contents, those particles fail to pass through the sand control screen and gradually accumulate and block the screen by forming a mud cake, which greatly reduce the permeability of the screen and limite sand production as well as gas and water production. Our research lays a foundation for sand production prediction and sand control scheme selection during gas recovery from clayey silty hydrate reservoirs that greatly need to consider a balance between sand control and gas productivity.

In chemical enhanced oil recovery (CEOR), it is very important to utilize the excessive usage of chemicals. A great opportunity lies in adopting natural surfactants, since it is cheaper, ecosystem friendly, and less toxic than their counterpart synthetic surfactants. Despite the availability of natural surfactant sources, it is yet very early to decide on their applicability. Therefore, this research focuses on natural-saponin extracted from different raw materials available in the Middle East and their interaction with quartz-sand. A special focus was given to the adsorption isotherm models to describe the interaction with the reservoir rocks.

Three raw materials were investigated are fenugreek, sugar beet leaves and chickpeas. The main extraction method employed was the chemical extraction using the soxhelet. The study used Uv-vis spectrometer to investigate the micellization behaviour and the consequent adsorption on quartz-sand. The presence of triterpenoid saponin is found dominant in all the sample, the intensity and purity differed according to the raw material source. Tthe critical micelle concentration (CMC) was at a close range of 4-5.5 wt% in all the samples. The highest adsorption was obtained by sugar beet leaves which is 192 g/kg. It is 25% and 37% higher than the Fenugreek and chickpeas, respectively. Increasing the salinity resulted in adsorption reduction between 2% and 56%. For the adsorption isotherms, it showed good agreement with the Langmuir model fitting. The remarkable finding is that the sugar beet leaves heterogeneous model seems to be valid by Frendluich and Halsey isotherms.

A new quantitative risk assessment method for hot work is proposed based on the analytic hierarchy process (AHP) and fuzzy comprehensive evaluation (FCE). It can help pipeline companies realize the risk management of hot work and further ensure the safe operation of oil and gas pipelines. Taking one natural gas pipeline in China as an example, this paper evaluates the risk of a single hot work in the spring of one natural gas pipeline in a high consequence region. First of all, the risk factors are determined with reference to the job safety analysis (JSA), and then experts were invited to fill out a questionnaire to collect their opinions. According to the results of the questionnaire, AHP is used to calculate the weight coefficients of the evaluation indicators, and FCE is used to evaluate the risk level of hot work. After calculation, the comprehensive risk score of hot work is 40.888. It belongs to a "general risk". This method can not only quantitatively evaluate the risk levels of hot work, but also reasonably sort the importance of various risk factors. It is helpful for the effective management of hot work and provides suggestions for implementing control measures.

In order to explore the effect of piston cup structure on its sealing characteristics and mechanical properties, a numerical simulation model of the piston cup in the BW-160 mud pump was established. Effects of work load, friction coefficient and cup structure parameters on the sealing and mechanical properties of the piston were discussed under mud discharge condition. The results show that stress concentration on the root and lips of the cup is becoming more and more obvious with the working load increases. The average contact pressure increases with the friction coefficient increases, but an excessive friction coefficient accelerate the wear of the cup and the heat generation. Effect of the piston lip interference and thickness on the sealing performance of the cup is greater than that of the inner wall width. The piston with groove structure can effectively improve the sealing performance of the piston. The mechanical properties of triangular groove cup are better than that of semicircular and trapezoidal groove cup.

Permeability is a measure of fluid transmissibility in the rock and is a crucial concept in the evaluation of formations and the production of hydrocarbon from the reservoirs. Various techniques such as intelligent methods have been introduced to estimate the permeability from other petrophysical features. The efficiency and convergence issues associated with artificial neural networks have motivated researchers to use hybrid techniques for the optimization of the networks, where the artificial neural network is combined with heuristic algorithms.

This research combines social ski-driver (SSD) algorithm with the multilayer perception (MLP) neural network and presents a new hybrid algorithm to predict the value of rock permeability. The performance of this novel technique is compared with two previously used hybrid methods (genetic algorithm-MLP and particle swarm optimization-MLP) to examine the effectiveness of these hybrid methods in predicting the permeability of the rock.

The results indicate that the hybrid models can predict rock permeability with excellent accuracy. MLP-SSD method yields the highest coefficient of determination (0.9928) among all other methods in predicting the permeability values of the test data set, followed by MLP-PSO and MLP-GA, respectively. However, the MLP-GA converged faster than the other two methods and is computationally less expensive.

The Keshen gas field is one of the most important natural gas supply sources in the Tarim basin, western China. The main gas producing interval there is the Lower Cretaceous Bashijiqike Formation(K₁bs), it is an ultra-deep tight reservoir whose buried depth exceeds 6000 m, and it shows a low matrix porosity (<10%) and extremely low matrix permeability (<0.1mD). However, this reservoir can supply extremely high and stable gas production due to improvement of reservoir quality by tectonism and fluid.

Based on tectonic evolution analysis by plenty of lab data of core plugs or thin sections, the enhancement models of tectonism and fluid are built, evidence suggests both tectonism and fluid improve the reservoir quality greatly. Tectonic evolution produces lots of natural fractures in 3stages which promote the ultra-deep tight reservoir permeability 10-200 times, then, testing results of new boreholes without fracturing show reservoir permeability underground can reach 20 mD. Furthermore, fluid dissolution increases reservoir porosity 1-2 times, the main dissolved mineral is feldspar, all fluid dissolution came from the unconformity controlling the dissolution distance. Tectonism and fluid interact on each other: Tectonism controls fracture distribution and types of diagenic fluid in reservoir, but fluids influence fracture cements and dissolution. Both tectonic folding and the fluid flow control the sweet point reservoir located in upper 150 m formation.