Consideration of Damaged Zone in a Tight Gas Reservoir Model With a Hydraulically Fractured Well

Abstract

Summary This paper provides a detailed description of conditions in the hydraulically damaged fracture environment after closure and how to integrate them into a reservoir-simulation model. A special model-initialization algorithm was developed and realized in a support tool to make possible the computing of a post-fracture performance in tight gas formations by a reservoir simulator. The input represents the treatment schedule of the fracturing process and some results produced by commercial fracturing packages or geophysical measurements. To represent the fracture geometry and properties, the information about the distribution of the proppant concentration in the fracture as well as the fracture-width variation is translated into the permeabilities and porosities of the fracture gridblocks. To determine the fracturing-fluid saturation in the invaded zone, a new approach was derived to imitate the fracture propagation at a fracturing period under consideration of the leakoff processes. The penetration of the fracturing fluid into the matrix was modeled by the Buckley-Leverett equations for two-phase nonmiscible displacement, with boundary conditions provided by a classical leakoff theory. The approach is illustrated with a simulation model prepared for the analysis of the cleanup process in a damaged fractured well within a Rotliegende tight gas formation in north Germany. Introduction The fluid that leaked off into the tight gas formation during the fracturing treatment may significantly suppress gas production because of the two-phase flow effects and the capillary end effect between the reservoir and fracture (Holditch 1979). Therefore, for more plausible evaluation of hydraulic fracture stimulation, an accurate representation of the flow in the immediate fracture environment becomes a necessity. In terms of numerical simulation of post-fracture well performance, the problem can be addressed by (1) an adequate representation of the fracture in a reservoir simulator and (2) a reasonably accurate picture of the initial fluid distribution around the fracture.

Proppant transport in dynamically propagating hydraulic fractures using CFD-XFEM approach

“…Some of the simulation studies based on GOHFER [16][17][18] also has the same limitation. Behr et al 19 and Shaoul et al 20 further developed the work and proposed an approximate model integrating the fracture propagation and reservoir simulation, by importing the propped-fracture geometry in the commercial reservoir simulator. However, only the uniform proppant distribution is assumed in the analysis, and the dynamic effects of proppant transport and distribution were neglected in the modelling.…”

“…Comparison of proppant distribution against fracture height at two different locations for varying injection rates Fig. 19. Comparison of proppant horizontal velocity against fracture height at two different locations for varying injection rates Another innovative approach that can aid in the success of hydraulic fracturing design by preventing the fracture tip screenout and more extended proppant transport is injecting the proppants intermittently and controlling the injection rate.…”

Evaluation of numerical schemes for capturing shock waves in modeling proppant transport in fractures

“…Later, several researchers used this approach in their numerical simulation of proppant transport. Behr et al (2006), Shaoul et al (2007) and Miranda et al (2010) linked a commercial reservoir simulator to a commercial fracture and proppant simulator and used the same concept that Settari et al (1990) had used for frac pack analysis. Although the linking of proppant and fracture simulators was novel, the proppant transport in these works was not numerically modeled by solving the mass balance hyperbolic PDE.…”

Prediction of Multistage Fracturing Performance in Horizontal Heavy Oil Carbonate Reservoir

“…However, the requirement for small grid sizes to represent fractures exhausts computational power and cause serious stability limitations in multiphase flow (Ji et al 2004). Integrating reservoir two-phase flow with fracture mechanic model (Settari 1980) and dynamic fracture properties (Behr et al 2006) had been tried using different grid refinement methods and reservoir simulation techniques. There exist even more complex models that couples the fracture geometry design and reservoir simulator in a synergetic mode (Lolon et al 2007).…”