Efficient Modelling Of Wellbore Backflow

Abstract

Production from reservoirs with large permeability contrasts or reservoirs consisting of several non-communicating layers can result in significant crossflow between the layers through multilayer wells. This entails the backflow of reservoir fluids from the wellbore to the reservoir. Standard line source/sink methods for handling wells in reservoir simulators are unable to cope with backflow because the wellbore is assumed to have the same saturations as the reservoir. To simulate backflow accurately, the well model must keep track of the fluid saturations within the wellbore. In this work, the discretized wellbore model developed by Collins et al. (1992) is extended and applied to vertical wells exhibiting backflow. The method described calculates fluid saturations along the wellbore implicitly. Comparisons of results between the standard line source/sink well model and the discretized wellbore model are made for several field-scale cases. It was found that the standard line source/sink model can result in unphysical values compared to the discretized wellbore model, which always yielded realistic production rates for the cases considered. Introduction Production from highly stratified reservoirs or from reservoirs with barriers between different production zones can result in significant backflow in producing wells. This corresponds to the flow of fluids from the wellbore back into the reservoir. This process happens quite frequently when the well is completed over multiple reservoir layers with poor vertical communication. The poor communication causes the potential gradient in the reservoir to be very different from the gradient in the wellbore. As the well acts as a channel for fluid flow between reservoir regions with different potentials, backflow occurs when the difference between the reservoir pressure and the wellbore pressure (pressure drawdown) becomes negative. Reservoir simulators where the well is represented as a line source/sink are not suitable for handling backflow. They give erroneous results, and when backflow is severe, they yield an unphysical solution. Holmes (1983) attempted to improve the source/sink representation of the well for backflow situations by including a global wellbore mass balance. In this approach, the fluid properties and saturations were assumed uniform throughout the wellbore. Modine and Coats (1990) introduced a superposition method in which fluid compositions resulting from an explicitly calculated head within the wellbore were used to determine individual layer inflow (layers producing into the wellbore) and outflow (layers receiving fluids from the wellbore). An efficient technique for modelling wellbore dynamics in reservoir simulation was developed by Collins et al. (1992). The wellbore flow equations were cast judiciously in a form similar to the reservoir flow equations. Thus, efficient techniques that were developed to solve the reservoir flow equations can readily be applied. Since Collins et al. considered horizontal production wells only, their method required extension to the case of vertical producers and injectors. This method will be referred to as the "discretized wellbore" technique. In this paper, the discretized wellbore technique is extended to vertical production/injection wells exhibiting backflow. Several field-scale cases are used to test the technique.

A Digital Twin-Based Approach for Optimization and Prediction of Oil and Gas Production

“…Leary, Peter et al [7] introduced the prospect of rock flow stimulation in the basement of enhanced geothermal system (EGS) by using wellbore temperature data, and the effective modeling of wellbore backflow was introduced by Sharma et al [8]. e related research on oil well pump simulation has been reported in literature, such as the simulation study of a double acting reciprocating oil well pump based on AMESim carried out by Wuhan Second Ship Design and Research Institute [9], and Northeast Petroleum University [10] has carried out numerical simulation calculation on the clearance flow and valve clearance flow model of oil well pump based on CFD technology, and the calculation results are visualized. e digital twin system of centrifugal pump disclosed by Siemens AG [11] of the United States patent right is established.…”

Research Trends of Cross-flow Behaviors and Production Characteristics in a Multi-layered Reservoir

“…유체를 생산중이거나 폐쇄(shut-in)상태 에 있는 유정에서는 각 층간의 추가적인 압력차이를 분 석함으로써 시추정 층간유동을 감지할 수 있다 (Petricola and Watfa, 1993;Pederson et al, 1998;Zhu et al, 2002;Sommerauer and Zerbst, 2006). 이산 시추정 모델 (discretized wellbore model)은 시추정 층간유동을 모사 하기에 적합한 것으로 알려져 있다 (Sharma et al, 1996). 두 개의 층으로 이루어진 다층 저류층에서 수직정을 통해 하나의 층만 천공 하였을 경우, 해당 층에서만 유체 의 생산이 이루어진다.…”