Integrated Wellbore/Reservoir Dynamic Simulation

Abstract

A comprehensive dynamic wellbore/reservoir flow model is successfully built by implicitly coupling a wellbore flow model with a near-wellbore reservoir model. The integrated model can be used to simulate various well flow transients that are subject to wellbore/reservoir dynamic interactions. In order to evaluate its performance, several hypothetical cases, such as well shut-in/start-up, heading, coning, and crossflow, are simulated. Comparison is made between the integrated approach and the conventional IPR approach, and the advantage of using the integrated model is justified. With given completion details and early-time reservoir data, the integrated model is then used to simulate a pressure buildup and drawdown test of an appraisal gas well. The simulation results show that the model can easily and accurately match the well testing data only by tuning the skin factor, which indicates the integrated model is suitable for optimizing well testing design, assisting well testing interpretation, and estimating the BHP where downhole measurements are not cost-effective and reliable. Introduction Conventional dynamic well flow models use steady-state IPRs to describe the influx of oil and gas from the reservoir, which ignore the flow transients in the near-wellbore area. On the other hand, reservoir models use steady-state lift curves to represent the TPRs, which ignore the flow dynamics in the wellbore. Neither the well models nor the reservoir models can account for the dynamic wellbore/reservoir interactions. For example, Gaspari[1]et al. verified the performance of an advanced transient multiphase flow model with the field data from an offshore well in Brazil. Even though the simulation matched the steady-state production perfectly, the model failed to simulate the shut-in/start-up operation by a big deviation in the downhole shut-in pressure prediction. This was attributed to the strong pressure transient in the tight reservoir, which was not considered in the modeling. To bridge this modeling gap, many efforts[2~15] have been made in developing integrated transient wellbore/reservoir models. These modeling efforts were related to the simulation of well testing[2,4,6,7,8,10,11,15], heavy oil thermal recovery[5], long horizontal well performance[3,9], and unstable well flows[12,13,14]. Despite most of the models have been very successful in simulating the special cases that they were developed for, they are lack of the general applicability for being used in a much wider scope due to either a poor wellbore flow model was used, or a simple reservoir description was adopted, or the numerical coupling between the wellbore and reservoir models was not properly handled. For example, one of the latest efforts from Ballard[14]et al. was intended to couple a comprehensive well flow model with a comprehensive reservoir model for investigating formation heading and liquid loading in a gas well that produces from a fractured tight reservoir. The coupled system is really advanced in terms of the modeling capabilities of the wellbore and reservoir models. However, the simulation speed had to be kept very slow in order to assure the coupling numerical stability, which was based on an explicit procedure. Some previous modeling efforts tried to solve the whole wellbore/reservoir system in one unified numerical scheme that could skip the coupling issues between the two models. This can only be achieved by sacrificing the modeling details of either the wellbore or the reservoir, e.g. by attaching an analytical solution of the reservoir model to the wellbore flow model, or by attaching a simple wellbore model to the reservoir model. However, this approach is not practical when the models on both sides of the sandface need to be comprehensive, particularly, when they are made to deal with the complexity of the modern advanced wells. The multiphase flow in wellbore and in porous medium is fundamentally different in nature, which requires separate modeling formulations and different numerical solution schemes. This paper is concerned with the development and testing of a novel integrated wellbore/reservoir model, which is achieved by implicitly coupling an existing transient wellbore flow model with an existing near-wellbore reservoir model. As both the two models are already comprehensive and powerful in their functionalities, the main focus of this work is on the numerical coupling between the two models and testing the usability of the integrated simulator. The detailed introduction of the models and their integration are given below.

Simulation of Multiphase Fluid-Hammer Effects During Well StartUp and Shut-In

“…To describe the inlet boundary condition accurately and to justify the advantage of using an integrated approach for simulation of various well flow transients, Hu et al (2007) dynamically coupled a wellbore flow model with a near-wellbore reservoir model, and presented an iterative simulation workflow, as shown in Fig. 2.…”

“…Bendiksen et al (1991), Han et al (2002), and Zhang and Vairavamoorthy (2005) have hence proposed different mechanistic models that considered not only pressure, flow rate, and temperature profile along the wellbore and flowline, but also phase redistribution in the nearwellbore region. Coats et al (2003), Hu et al (2007), and Zhang et al (2010) conducted further studies by coupling subsurface and surface models implicitly and explicitly. Their findings have been applied for integrated field-development planning and flow-assurance studies, especially liquid-loading and liquid-slugging problems.…”

Coupled simulation of near-wellbore and reservoir models

“…In the literature, some studies have been performed on the coupled modelling between a wellbore flow model and a reservoir model (see, for example, Johansen and Khoriakov, 2007;Hu et al, 2007;Nennie et al, 2007;Pourafshary et al, 2009;Livescu et al, 2010). During the production, the multiphase flow commonly occurs in different sections of a flow-line such as the pipe, the tubing and the wellbore.…”

Integrated Wellbore/Reservoir Model Predicts Flow Transients in Liquid-Loaded Gas Wells

“…Some cases above are addressed in a separate publication [2] using the same integrated model introduced in this paper. Some cases above are addressed in a separate publication [2] using the same integrated model introduced in this paper.…”