Geofluids最新文献

Formation pressure and mobility represent two fundamental parameters that are essential for the development of oil and gas resources. These parameters can be obtained in real time through the process of formation testing while drilling (FTWD). It is highly probable that the drilling fluid will invade the formation during the FTWD process. Nevertheless, the prevailing theory regarding FTWD assumes that the wellbore is impermeable, thereby rendering its potential impact on FTWD and mobility inversion unclear. Therefore, to clarify the influence of the permeable wellbore on FTWD and mobility inversion, a mathematical model of FTWD seepage was first proposed by involving the permeable wellbore. Secondly, the finite element method was used to solve this model, and this model was verified by using the analytical models. The pressure response curves and isobaric surface near the FTWD probe were then compared for both the permeable and impermeable wellbores, and the influence of the permeable wellbore on the pressure response curves of FTWD was analyzed. Finally, the method of integral area was used to invert mobility, and the compressive influence of different factors on both the pressure response curves and mobility inversion was discussed for both the permeable and impermeable wellbores. The results indicated that the permeable wellbore has a significant impact on the pressure response curves and isobaric surface near the probe due to the limited pressure sweeping range around the probe and the invasion of drilling fluid. In the case of a permeable wellbore, the invasion of the drilling fluid into the formation can cause a supercharge effect around the well. This effect can cause an initial increase followed by a decrease in the pressure buildup phase. The pressure buildup always exceeds the original formation pressure, which can lead to an overestimation of the measured formation pressure compared to the original. Meanwhile, the permeable wellbore can also lead to an overestimation of the inversion mobility, but the impermeable wellbore has much less influence on the mobility inversion. To improve inversion accuracy, it is recommended to increase the rubber packer radius, lengthen the suction period, reduce the storage volume of the pipeline, and decrease the overbalanced pressure. However, these measures cannot mitigate the impact of the supercharge effect on formation pressure testing. This paper provides theoretical guidelines for the use of FTWD tools and data interpretation.

In the article titled “The Conformal Finite-Difference Time-Domain Simulation of GPR Wave Propagation in Complex Geoelectric Structures” [1], the postal code in Dazhong Chen’s affiliation was incorrectly shown as 450001 and should be corrected as above to 450016.

Water inrush disaster is one of the most severe problems during the construction of sea tunnels, primarily due to faults, karst, and weathered zones. Once a water inrush disaster occurs, it can lead to construction delays, traffic disruptions, and major economic losses, as well as potential consequences such as seawater intrusion, casualties, project suspension, and tunnel closure. Thus, advanced geological prediction is indispensable. During the construction of the Shantou Bay subsea tunnel, a sudden water inrush accident occurred in the sea–land transition section. To prevent such incidents and ensure safety, an integrated approach was employed. Firstly, the cross-hole resistivity method was used to predict water content in front of the tunnel, as it is highly sensitive to water. Subsequently, borehole ground-penetrating radar was applied to finely characterize the geological structure. By combining these two methods, the size, scale, location, water content, and spatial distribution of water-bearing structures in front of the tunnel were identified. With the above measures, the Shantou Bay subsea tunnel passed through the detection section successfully. Herein, we present a case study and offer a valuable reference for similar projects concerning subsea tunnel construction.

The nonhomogeneity of conglomerate in terms of organization and the complexity of fracture extension make the design and effective implementation of fracturing in conglomerate reservoirs challenging. Considering the limitations of physical experiments and two-dimensional (2D) numerical modeling, this paper adopts the continuum-discontinue element method (CDEM) to carry out numerical simulation of three-dimensional (3D) conglomerate fracturing considering pore-fracture seepage. By introducing multiple parameters to quantify the correlation between fracture geometry, fracture complexity, and damage mode, the evolution mechanism of fracture morphology under the influence of multiple factors is systematically investigated. The results show that the numerical simulation experiments can control the variables well, but the random distribution of gravel leads to the unpredictability of fracture extension, and the concluding patterns obtained still show large fluctuations. The high permeability of the gravel promotes the development of gravel-penetrating fractures but has less effect on the overall morphology of the fractures. High-strength gravel promotes the development of branching fractures in the initiation phase, which acts as a barrier to expanding fractures, and the most complex fracture development occurs when the gravel strength is approximately 4–5 times that of the matrix. In the weakly cemented state, fracture development around the gravel contributes to the shear failure of the conglomerate, but the strength of the cemented interface has no obvious control on the overall fracture morphology. The correlation between gravel content and conglomerate damage mode is significant, with the highest degree of fracture complexity occurring when the gravel content is approximately 30%. Stress differential is the most significant controlling factor affecting fracture morphology, followed by minimum principal stress. When the stress difference reaches 8 MPa, the fracture morphology begins to stabilize, and too high a stress difference will cause the phenomenon that the fracture stops expanding, affecting the fracturing effect. A high level of minimum stress promotes tensile failure in conglomerate, and the scale and complexity of fracture decrease. High injection displacement promotes branch fracture development and reduces the effect of in situ stress on fracture extension, and too high a displacement leads to inhibition of main fracture development.

The stability of the plugging zone has a great impact on lost circulation control and gas invasion prevention in fractured reservoirs. In this work, the concept of “cavitation-induced shear failure” is put forward based on the analysis of the flow field characteristics, and the failure mechanism is discussed. The strength physical model of a fractured plugging zone is formed based on the analysis of the characteristic parameters of LCMs and the failure mechanism. And then the simulation experiments of cavitation-induced shear failure, gas invasion prevention, pressure bearing, and tight plugging are carried out. The research shows that (1) the fractured plugging zone is a dense granular matter system, and the contact forces and quid bridge force are dominant in its internal; (2) the cavitation-induced shear failure is one of the main failure modes of the plugging zone in a fractured gas reservoir, and the failure process includes three steps: gas diffusion-dilution damage, confluence and carry damage, and displacement dislocation shear failure; (3) the strengthening model of the plugging zone, “rigid bridging+elastoplastic filling+lacing wire of fiber+film-forming seal,” is a better model, and experiments prove that it can form a tight pressure-bearing plugging zone, preventing drill-in fluid loss. The research results provide a theoretical and technical basis for the lost circulation control of fractured gas formations.

The importance of production performance forecasting in reservoir development and economic evaluation cannot be overstated. Previous models have shown deficiencies in accurately predicting production performance, necessitating the development of a new semianalytical model to enhance its application scope and prediction accuracy. This study proposes a novel semianalytical model based on the Buckley–Leverett (BL) equation and a newly proposed linear relationship between outlet water saturation and average water saturation, as well as Willhite’s formula of oil/water relative permeability. The results demonstrate the universality of this new model, as it can generate three equivalent log-linear relations, including the previously proposed model. Sensitivity analysis confirms the applicability of the model in various reservoirs. In addition, both model and field case studies highlight the advantages of this technique in forecasting water cut and cumulative oil production, with an extensive application scope covering over 90% of the water cut range. A comparison of oil production prediction results from six different predictive methods reveals that the proposed semianalytical model exhibits the lowest error rate of −0.01%. Moreover, the semianalytical model can be utilized to directly solve for the approximate values of the exponents in Willhite’s oil/water relative permeability equations. In summary, this novel semianalytical forecasting model demonstrates a robust ability to forecast water cut, cumulative oil production, and recovery efficiency.

The Chang 9 oil layer deposits within Ansai District, Ordos Basin, yield considerable reserves of crude oil, yet their source remains ambiguous. This research endeavor was designed to characterize the Chang 9 crude oil and the Chang 7 and Chang 9 source rocks (SRs) of the Yan-Chang Formation via organic geochemical analysis. The results indicate that the Chang 9 crude oil exhibits a Pr/Ph ratio of 0.84–2.29 and Ga/C₃₀H less than 0.1, implying formed in a weak reduction to weak oxidation freshwater environment. The regular sterane C₂₇-C₂₈-C₂₉ configuration assumes an inversed “L” type, reflecting mixed sources and dominant terrestrial plant input. Ratios such as C₂₉20S/(20S + 20R) (0.54–0.6) and C₂₉ββ/(ββ + αα) (0.44–0.58) indicate a mature oil stage. The depositional environment of the C7 and C9 SRs is similar, with weak oxidation to reduction conditions, and consists mainly of Type I and II organics, with a relatively higher maturity of the C9 SRs. A difference in C₁₉/C₂₃TT and C₃₀D/C₃₀H was found between the C7 and C9 SRs. The results show that the C9 crude oils have a similar C₁₉/C₂₃TT with the C9 SRs and similar diahopanes distribution with Class II SRs (C7 and part of the C9 SRs). Thus, the C9 crude oils most likely originate from the C9 SR mixed with the C7 SRs.

As urbanization gathers pace, projects involving adjacent subway tunnels are increasing, thereby amplifying the need for robust tunnel protection measures. Currently, there exists a notable lack of precise analyses on the three-dimensional (3D) deformation laws and mechanisms of tunnels affected by adjacent deep excavation. Moreover, the influence patterns of retaining wall stiffness and deep excavation depth on the 3D deformation of pit-side tunnels remain unclear. The purpose of this research is to bridge the existing disparity by adopting the hypoplastic model, which effectively captures soil stiffness that is dependent on soil state, strain, and stress path, even at small strains, as well as soil strength, based on reported centrifuge model tests. This approach facilitates a comprehensive, precise numerical analysis of the interaction between deep excavation and preexisting tunnels located outside the retaining wall. The analysis sheds light on the deformation mechanisms and trends of pit-side tunnels not solely confined to the longitudinal axis but extending to the transverse plane as well, while systematically examining the influence of varying excavation depths and retaining wall stiffness on key tunnel parameters, including longitudinal deformation, diameter changes, bending strains, and soil pressure distributions around the tunnels. The study reveals that if the tunnel situated outside the retaining structure lies beneath the foundation pit’s base, deep excavation only slightly deforms the tunnel. However, when the tunnel outside the retaining structure is positioned above the pit’s base, its deformation progressively intensifies with deeper excavation, but the growth rate has a decreasing trend. An enhancement in the stiffness of the retaining wall results in a notable decrease in the deformation exhibited by the adjacent tunnels. The findings contribute to a deeper understanding of the complex responses of pit-side tunnels to excavation activities, ultimately facilitating the design and construction of safer and more resilient urban subway infrastructure.

An investigation of the distribution and control factors of groundwater is significant for the rational exploitation and utilization of groundwater resources. This study analyzes the hydrogeochemical processes and control factors of shallow groundwater in the Guohe River Basin. A hydrogeological survey was conducted, and hydrochemical and hydrogen–oxygen isotopic data of 125 samples of surface water and groundwater were analyzed. The results showed that the total dissolved solid (TDS) content in shallow groundwater was 138–2967 mg/L, with an average of 831 mg/L. A decline in the TDS was observed from the upper to the lower reaches. The contents of the anions and cations in the shallow groundwater were in the order HCO₃⁻ > Cl⁻ > SO₄²⁻ and Na⁺ and K⁺ > Mg²⁺ > Ca²⁺, respectively. The cation exchange increased the aqueous concentrations of Na⁺ and K⁺, and the TDS content was highly correlated with the contents of Na⁺, Cl⁻, and SO₄²⁻ ions. The δD and δ¹⁸O values in shallow groundwater increased from the upper to the lower reaches, with the mean δD values being −59.72‰, −53.58‰, and −47.17‰ and the mean δ¹⁸O values being −8.33‰, −7.37‰, and −6.43‰. The contribution rates of the recharge source, evaporation, and water–rock interaction to the groundwater TDS concentration were 20.4%, 29.5%, and 50.1%, respectively. The water–rock interaction dominated the formation of shallow groundwater in the Guohe River Basin. The dissolution of salt rock and gypsum contributed to ion formation in shallow groundwater. The research findings can be used to improve the groundwater quality in the Guohe River Basin.

The aim of this study is to improve hydrocarbon reservoir estimation by combining the deterministic and probabilistic approaches in an improved volumetric model with the objective of reducing geological uncertainties and achieving better reserve estimations. The case study was made in the Rio Del Rey basin of Cameroon. To achieve this goal, a mathematical model was built using the volumetric expression of the stock tank original oil in place (STOIIP), the Raymer–Hunt expression of porosity and transit time, and the Simandoux model modified by the Schlumberger expression of water saturation. The application and validation of the proposed model were made through Interactive Petrophysics, Petrel software, and Monte Carlo simulation on Minitab Workspace. The results obtained by a deterministic approach on the investigated area of 2000 m² give a total estimated quantity of oil in place of 11897.67 MMbbl, a total estimated quantity of gas in place of 27.79 Bcf, a total estimated quantity of recoverable oil of 3606.28 MMbbl, and a total estimated quantity of recoverable gas of 19.52 Bcf. The probabilistic approach permitted to obtain an estimated quantity of oil in place of 150194141.45 MMbbl. In this study, it appears that the net value added is $288,898,222. This therefore confirms the accuracy of the model and the profitability of the project.