Flowing Material Balance and Rate-Transient Analysis of Horizontal Wells in Under-Saturated Coal Seam Gas Reservoirs: A Case Study from the Qinshui Basin, China

Suyang Zhu,Alireza Salmachi

doi:10.3390/en14164887

Suyang Zhu, Alireza Salmachi

Open Access

https://doi.org/10.3390/en14164887

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Abstract

Two phase flow and horizontal well completion pose additional challenges for rate-transient analysis (RTA) techniques in under-saturated coal seam gas (CSG) reservoirs. To better obtain reservoir parameters, a practical workflow for the two phase RTA technique is presented to extract reservoir information by the analysis of production data of a horizontal well in an under-saturated CSG reservoir. This workflow includes a flowing material balance (FMB) technique and an improved form of two phase (water + gas) RTA. At production stage of a horizontal well in under-saturated CSG reservoirs, a FMB technique was developed to extract original water in-place (OWIP) and horizontal permeability. This FMB technique involves the application of an appropriate productivity equation representing the relative position of the horizontal well in the drainage area. Then, two phase (water + gas) RTA of a horizontal well was also investigated by introducing the concept of the area of influence (AI), which enables the calculation of the water saturation during the transient formation linear flow. Finally, simulation and field examples are presented to validate and demonstrate the application of the proposed techniques. Simulation results indicate that the proposed FMB technique accurately predicts OWIP and coal permeability when an appropriate productivity equation is selected. The field application of the proposed methods is demonstrated by analysis of production data of a horizontal CSG well in the Qinshui Basin, China.

Highlights

Published: 10 August 2021Hydraulic fracturing and horizontal well completion are effective approaches to stimulate reservoirs, and enhance well productivity in coal seam gas (CSG) reservoirs, respectively [1,2,3]
In our previous study [32], we showed that the application of the area of influence (AI) in the analysis of formation linear flow of a hydraulically fractured CSG well resulted in a more accurate estimation of the fracture half-length compared to the
We introduce the AI for both early radial flow and formation linear flow regimes for a horizontal well in an under-saturated CSG reservoir

Summary

Introduction

Published: 10 August 2021Hydraulic fracturing and horizontal well completion are effective approaches to stimulate reservoirs, and enhance well productivity in coal seam gas (CSG) reservoirs, respectively [1,2,3]. An effective tool to estimate reservoir and stimulation information of horizontal wells is the modern production data analysis (PDA), including rate-transient analysis (RTA) and flowing material balance (FMB) techniques. Both techniques are powerful methods for reservoir characterization in unconventional reservoirs, such as tight gas, shale gas, and dry CSG reservoirs, when single-phase flow occurs [1,4,5,6]. In the production data analysis (single-phase flow), a diagnostic curve is plotted using rate-normalized pressure (RNP) and pseudo-time to identify the flow regimes [1,7,8,9]. The gas desorption impact on pressure is considered in material balance pseudo-time using desorption compressibility, which is included in the total compressibility as an independent term [10,11]

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