Construction and Application of a Big Data System for Regional Lakes in Coalbed Methane Development.

With the rapid development and widespread application of big data and artificial intelligence, the upgrading of digital and intelligent industries has been rapidly popularized in the oil and gas industry. First, based on the theory of ″regional data lake″, the digital nature of the CBM governance system is analyzed, and the optimization model of CBM governance for different data types is established. Second, considering the geological characteristics and development mode of the CBM reservoir, the regional data lake expansion model is established. Third, a theoretical model of coupling ″on-site data, laboratory data, management data, and data management system″ has been established. The research shows the following: (a) The CBM governance system based on the regional data lake can be divided into four parts: basic support, data life cycle, core governance areas, and governance strategy support. (b) The coupling of the coalbed methane governance model with the BP neural network model in this article has good application results. (c) The computational efficiency of this model has been improved by 12%, which has broad application prospects.

Experimental Investigation on Spontaneous Imbibition of Surfactant Mixtures in Low Permeability Reservoirs.

Spontaneous imbibition of surfactants could efficiently enhance oil recovery in low permeability sandstone reservoirs. The majority of studies have considered the application of individual surfactants to alter wettability and reduce interfacial tension (IFT). However, a significant synergistic effect has been reported between different types of surfactants and between salts and surfactants. Therefore, this study systematically studied the capability of a binary surfactant mixture (anionic/nonionic) and a ternary surfactant mixture (anionic/nonionic/strong base-weak acid salt) in imbibition enhanced oil recovery (IEOR). The interfacial properties and the cores' wettability were explored by IFT and contact angle measurements, respectively. Subsequently, the imbibition performances of different types of surfactant solutions were discussed. The results suggested that the surfactants' potential to enhance oil recovery followed the order of ternary surfactant mixture > binary surfactant mixture > anionic > nonionic > amphoteric > polymer. The ternary surfactant mixture exhibited strong capacity to reverse the rock surface from oil-wet (125°) to strongly water-wet (3°), which was more significant than both binary surfactant mixtures and individual surfactants. In addition, the ternary surfactant mixture led to an ultralow IFT value of 0.0015 mN/m, achieving the highest imbibition efficiency (45% OOIP). This research puts forward some new ideas on the application of the synergistic effects of surfactants in IEOR from low-permeability sandstone reservoirs.

Novel Model for Rate Transient Analysis in Stress-Sensitive Shale Gas Reservoirs.

Technical advances in hydraulic fracturing and horizontal drilling technologies enable shale to be commercially exploited. Due to the technical and economic limitations of well testing in shale gas plays, rate transient analysis has become a more attractive option. After hydraulic fracturing, flow mechanisms in multiple scaled pores of shale become extraordinarily complicated: adsorption in nanopores, diffusion in micropores, and non-Darcy flow in macropores. Moreover, shale gas reservoirs are stress-sensitive because of ultralow permeability and diffusivity in a matrix. Furthermore, the porosity and permeability of natural fractures are stress-dependent as well. Accounting for all of these complex flow mechanisms, especially the aforementioned stress-sensitive parameters, a semianalytical production solution of a multiple fractured horizontal well (MFHW) can rapidly predict the entire production behavior. Scholars have done much work on the complex flow mechanisms of shale. Most models regarded permeability as a stress-sensitive parameter while diffusivity and porosity were considered to be a constant. However, diffusivity and porosity were proved to be stress-sensitive as experimental science developed. In this study, we present a novel semianalytical model for rate transient analysis of MFHW, which simultaneously incorporates multiple stress-sensitive parameters into flow mechanisms. Substituting stress-dependent parameters (diffusivity, porosity, and permeability) into governing equations resulted in strong nonlinearities, which was solved by employing the perturbation method. Production behaviors with only stress-sensitive permeability were compared with multiple stress-dependent parameters. The new model with multiple stress-sensitive parameters declined slower than the permeability-sensitive model, and the new model matched better with the field data. In addition, the effects of major stress-sensitive parameters on production decline curves were analyzed by the proposed model. The sensitivity analysis indicated that different parameters had their own degree of sensitivity intensity and influence on the production period. Finally, 1001 wells from the Marcellus shale play were divided into three well groups. Estimated inversion values of reservoir parameters from the three well groups and relevant single wells were consistent with the field data. The inverted values of single wells fluctuate within the inversion values of well groups, which indicates that the production behavior of well groups could be a guide for rate transient analysis of a single well in shale gas reservoirs.

Mechanism and multi-step kinetic modelling of Cr(VI) adsorption, reduction and complexation by humic acid, humin and kerogen from different sources.

Humin (HM) and kerogen (KG) are widespread in soils and sediments, which have strong retention effects on the migration and transformation of Cr(VI) in subsurface environment. Previous studies mainly focused on the interaction between Cr(VI) and soluble organic matter, such as humic acid (HA); however, the adsorption and reduction mechanism for Cr(VI) by insoluble HM and KG are still unclear, the processes of which might be quite different from HA due to their different sources and humification degrees. Consequently, in this study, HA, HM and KG extracted from different sources were used to explore the adsorption, reduction and complexation mechanisms of Cr(VI) in soils and sediments, based on which a multi-step kinetic model of Cr(VI) was carried out. According to the results, the retention of Cr(VI) by humus was found to obey a coupling mechanism of "adsorption-reduction-complexation", where Cr(VI) adsorption was by complexation with carboxylic groups by ligand exchange. The phenolic and hydroxylic groups were determined to be the main electron donor for Cr(VI) reduction. Notably, the Cr(III) produced was found to be adsorbed on the surface of humus by complexation on phenolic and hydroxylic groups, and the excesses were released into the liquid phase after the saturation of complexation sites. Based on the revealed mechanism, a multi-step kinetic model for simultaneously describing Cr(VI) adsorption and reduction and behaviour of Cr(III) was proposed producing a better fitting performance (R2 ≥ 0.984) than the first-order and second-order kinetic models (R2 ≤ 0.84 and 0.87, respectively) and hence could provide more factual understanding of Cr(VI) transformation in soils and sediments enriched in various types of humus.

Transport Behavior of Oil in Mixed Wettability Shale Nanopores.

Shale oil reserves play an important role in the oil & gas industry. The investigation of oil transport behavior in shale nanopores is crucial in the successful exploitation of shale oil reservoirs. However, the transport mechanisms of oil in shale nanopores are still not understood. In this paper, a model for oil transport through a single nanopore was established by considering mixed wettability, surface roughness, varying viscosity, and the effects triggered by adsorbed organic matter. The organic surface ratio of a single nanopore was used to quantify mixed wettability, while the effects of adsorbed organic matter were estimated by the surface coverage and the adsorption thickness. The entire mathematical model was simplified into several equations to discuss the contributions of each mechanism. The results showed that to accurately predict the oil transport properties in mixed wettability shale nanopores, it is necessary to consider varying viscosity, wettability alteration, and the oil molecule structure. Adsorbed organic matter led to increase in oil flow capacity by altering the surface wettability. However, the oil flow capacity was greatly reduced when varying viscosity was considered. Additionally, the contributions of each mechanism varied with the pore type. Furthermore, increasing surface roughness significantly reduced the oil flow capacity in both organic and inorganic nanopores. This work provides a better understanding of oil transport behavior in mixed-wettability shale nanopores and a quantitative framework for future research.

A novel non-ionic surfactant extract derived from Chromolaena odarata as shale inhibitor in water based drilling mud.

High performance clay swelling inhibitors play a vital role in improving inhibition characteristics of shales. The linkages between the inhibition's characteristics of the non-ionic surfactant extract from bio-based inhibitors are yet to be fully explored in the literature. This paper reports the use of a crude extract containing saponins from Chromolaena odorata (CO) leaf, which act as surfactants for inhibiting shale hydration. Determination of the inhibitive property of nonionic surfactant was made through measurements of surface-active properties, inhibition tests, filtration, rheological and strength test. The experimental findings on CO showed that it was highly compatible and very stable with conventional water-based drilling fluids (WBDFs), a highly effective shale inhibitor and a works through plugging and viscosity acting effect in the shale system.