查看更多>>摘要： The research of multiphysical thermal-hydraulic-mechanical (THM) simulation has achieved significant progress in the past decade. Currently, two types of approaches for poromechanical simulation co-exist in the reservoir simulation community, namely the stress approach with stress as the primary variable for the mechanical governing equations and the displacement approach with displacement as the primary variable. In this work, we aim to provide a theoretical foundation and a practical semi-analytical solution for the stress approach, which is based on the Navier-Beltrami-Michell Equations. Moreover, we will clarify the relationship (and equivalence) between the two approaches. We have proven the existence and uniqueness of the stress solution of Navier-Beltrami-Michell equation with given pressure and temperature field. Moreover, we have demonstrated the equivalence of the stress formulation to the displacement formulation. We have shown that the stress approach yields the same results as the displacement approach, but is more convenient to be implemented. We also conducted an a priori analysis of the mean stress solution. Based on Fourier's analysis, we have developed a general semi-analytical solution for thermal-hydraulic-mechanical process. The semi-analytical solution takes the pressure solution from the hydraulic simulation module (or a commercial reservoir simulator) and directly predicts the stress tensor of the multiphysical system. As such, the solution can be programmed fully coupled with the hydraulic simulation module to predict the stress field with varying pressure and temperature of homogeneous poroelastic rocks under given stress boundary conditions. From the work above, we have laid a theoretical foundation for the stress approach. The derived semi-analytical solution of the stress field shows excellent accuracy. The solution has been used to predict the transient stress field of a dual-porosity system during primary depletion. This paper is arguably the first trial in the petroleum engineering community to clarify the relationship between the stress approach and the displacement approach. Moreover, the derived semi-analytical solution provides a convenient yet precise way to obtain the stress field without time-consuming numerical simulation. 1
查看更多>>摘要： Lost circulation can be one of the most troublesome situations during drilling, especially in naturally fractured formations. This situation may lead to serious economic losses because of the loss of expensive drilling fluid into the formation and nonproductive time spent on regaining drilling ROP. Granular lost circulation materials (LCMs) are the most commonly used to prevent and cure lost circulations. However, poor understanding of how granular LCM works at a micro-scale has limited their effectivity. In this paper, we developed a coupled CFD-DEM model by combining computational fluid dynamics with discrete element methods to simulate the sealing process of LCM in a wedge-shaped fracture by tracking the motion of each individual particle. Formation and evolution of both the sealing zone and the resulting force chain network were investigated by combining micro process visualization and analysis of flow characteristic curves of LCM suspension injection. The results show that injected LCM particles eventually result in three situations after transport in the fracture, depending on their size and concentration: 1) no bridging no sealing, 2) bridging without sealing, and 3) bridging with sealing. The fracture sealing zone is formed by either single-particle bridging or dual/multi-particles bridging of LCMs. A successful sealing comprises four stages: 1) LCM suspension uniform flow, 2) unstable bridging, 3) sealing zone formation and growth, and 4) fluid flow through the porous sealing zone. These situations and evolutionary stages are clearly reflected in the morphological changes of the flow curve. The formation and evolution of the force chain network also include four stages: 1) discrete force chain dynamic initiation, 2) small force chain network unstable formation, 3) discrete force chain network aggregation, 4) force chain network stable propagation. Strong force chains are in the front section and weak force chains are in the middle and end section of the sealing zone. The formation and collapse of force chains within bridging particles determines if a bridging structure and a sealing zone can be formed and stable. Dual-particles bridging formed sealing zone is weaker than single-particle bridging one because of the weak point in the strong force chain in the fracture width's direction. This research provides a better insight into the process of fracture sealing by granular LCMs, which contributes to improve efficiency of lost circulation control jobs.
查看更多>>摘要： Multiple wellheads are required to be constructed in a confined space for drilling cluster wells, so it is necessary to take high-precision cross-well ranging measures to prevent borehole collisions. To solve the problem of ranging between the drilling wells and multiple adjacent wells, a new method of ranging between adjacent wells based on the casing current excitation of adjacent wells is proposed, in which low frequency excitation current is injected into the casing in adjacent wells with time-division or frequency-division excitation mode, and the ranging tool in the drilling well is used to detect the magnetic induction intensity generated by the casing current around the formation, so as to determine the distance between adjacent wells. In this paper, the algorithm for determining distances and directions between adjacent wells is established, and the key factors affecting the ranging model are analyzed by numerical simulations. The results show that with the increase of well depth, the magnetic induction decreases at the exponential rate of exp, and high formation resistivity and low excitation current frequency are beneficial to enhance the magnetic induction. The experimental results show that within the range of 10 m, the measured value of magnetic induction intensity matches well with the theoretical value, and the directional measurement error is less than 1°, which validates the effectiveness and accuracy of this method, and provides theoretical guidance and experimental basis for the development of anti-collision measurement while drilling system for cluster wells.
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