A Material Balance Equation for Stress-Sensitive Shale Gas Reservoirs Considering the Contribution of Free, Adsorbed and Dissolved Gas

Abstract Hydraulic fracture/reservoir properties and fluid-in-place can be quantified by using rate-transient analysis (RTA) techniques applied to flow rates/pressures gathered from multi-fractured horizontal wells (MFHWs) completed in unconventional reservoirs. These methods are commonly developed for the analysis of production data from single wells without considering communication with nearby wells. However, in practice, wells drilled from the same pad can be in strong hydraulic communication with each other. This study aims to develop the theoretical basis for analyzing production data from communicating MFHWs completed in single-phase shale gas reservoirs. A simple and practical semi-analytical method is developed to quantify the communication between wells drilled from the same pad by analyzing online production data from the individual wells. This method is based on the communicating tanks model and employs the concepts of macroscopic material balance and the succession of pseudo-steady states. A set of nonlinear ordinary differential equations (ODEs) are generated and solved simultaneously using the efficient Adams-Bashforth-Moulton algorithm. The accuracy of the solutions is verified against robust numerical simulation. In the first example provided, a MFHW well-pair is presented where the wells are communicating through primary hydraulic fractures with different communication strengths. In the subsequent examples, the method is extended to consider production data from a three-well and a six-well pad with wine-rack-style completions. The developed model is flexible enough to account for asynchronous wells that are producing from distinct reservoir blocks with different fracture/rock properties. For all the studied cases, the semi-analytical method closely reproduces the results of fully numerical simulation. The results demonstrate that, in some cases, when new wells start to produce, the production rates of existing wells can drop significantly. The amount of productivity loss is a direct function of the communication strengths between the wells. The new method can accurately quantify the communication strength between wells through transmissibility multipliers between the hydraulic fractures that are adjusted to match individual well production data. In this study, a new simple and efficient semi-analytical method is presented that can be used to analyze online production data from multiple wells drilled from a pad simultaneously with minimal computation time. The main advantage of the developed method is its scalability, where additional wells can be added to the system very easily.

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The material balance equation for fractured vuggy gas reservoirs with bottom water-drive combining stress and gravity effects

Journal of Natural Gas Science and Engineering ◽

10.1016/j.jngse.2017.04.027 ◽

2017 ◽

Vol 44 ◽

pp. 96-108 ◽

Cited By ~ 6

Author(s):

Zhouhua Wang ◽

Zidun Wang ◽

Fanhua Zeng ◽

Ping Guo ◽

Xinyue Xu ◽

...

Keyword(s):

Balance Equation ◽

Bottom Water ◽

Material Balance ◽

Material Balance Equation ◽

Gas Reservoirs ◽

Gravity Effects

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A Physics-Based Method To Forecast Production From Tight and Shale Petroleum Reservoirs by Use of Succession of Pseudosteady States

SPE Reservoir Evaluation & Engineering ◽

10.2118/167686-pa ◽

2015 ◽

Vol 18 (04) ◽

pp. 508-522 ◽

Cited By ~ 7

Author(s):

M. S. Shahamat ◽

L.. Mattar ◽

R.. Aguilera

Keyword(s):

Balance Equation ◽

Transient Flow ◽

Material Balance ◽

Petroleum Reservoirs ◽

Flow Equation ◽

Production Data ◽

Material Balance Equation ◽

Gas Reservoirs ◽

Initial Flow ◽

Shale Reservoirs

Summary Analysis of production data from tight and shale reservoirs requires the use of complex models for which the inputs are rarely known. The same objectives can also be achieved by knowing only the overall (bulk) characteristics of the reservoir, with no need for all the detailed and rarely known inputs. In this study, we introduce the concept of continuous succession of pseudosteady states as a method to perform the analysis of production data. It requires few input data yet is based on rigorous engineering concepts, which works during the transient- as well as the boundary-dominated-flow periods. This method consists of a combination of three simple and well-known equations: material balance, distance of investigation, and boundary-dominated flow. It is a form of a capacitance/resistance methodology in which the material-balance equation over the investigated region represents the capacitance and the boundary-dominated-flow equation represents the resistance. The flow regime in the region of investigation (the areal extent of which varies with time during transient flow) is assumed to be pseudosteady state. This region is depleted at a rate controlled by the material-balance equation. The initial flow rate and flowing pressure are used to define the resistance, and the distance of investigation defines the capacitance. The capacitance and resistance are then used in a stepwise procedure to calculate the depletion and the new rates or flowing pressures. The method was tested, for linear-flow geometry, against analytical solutions for liquids and numerical simulations for gas reservoirs, exhibiting both transient and boundary-dominated flow. Excellent agreement was obtained, thus corroborating the validity of the method developed in this study. Two practical examples are provided to demonstrate the applicability of the methodology to forecast production from tight and shale petroleum reservoirs. The proposed method is easy to implement in a spreadsheet application. It indicates that complex systems with complicated mathematical (e.g., Laplace space) solutions can be represented adequately by use of simple concepts. The approach offers a new insight into production analysis of tight and shale reservoirs, by use of familiar and easy-to-understand reservoir-engineering principles.

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