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Paper Number 95535-MS
DOI What's this? 10.2118/95535-MS
Title Interpretation of Multi-Hydraulically Fractured Horizontal Wells in Naturally Fractured Reservoirs
Authors Y. Bettam, Sonatrach PED; D. Tiab, Oklahoma U.; and A. Zerzar, Sonatrach HMD
Source SPE International Improved Oil Recovery Conference in Asia Pacific, 5-6 December 2005, Kuala Lumpur, Malaysia
Copyright 2005. Society of Petroleum Engineers
Language English
Preview Abstract
Horizontal wells are thought to be necessary in formations with low-permeability to increase the recovery and reduce the risk of drilling a dry hole. The horizontal well may cross natural fissures. Although hydraulically fracturing horizontal wells in such formations is a risky job, it may be necessary in order to achieve commercial production. This is especially true for naturally fractured gas reservoirs with matrix permeability in microdarcies and where natural-fracture network does not contribute considerably to the flow from the reservoir into the wellbore.
This study investigates the transient pressure behavior of a multiply fractured horizontal well (MFHW), as well as the long time performance of such a completion in an anisotropic naturally fractured reservoir of infinite extent.
Combining boundary element method and Laplace transform, single-fracture solution is considered first as it constitutes the core part of the multiple-fracture model. Then, a solution to multiply fractured horizontal wells is presented, which assumes fractures of distinct properties, it allows for unequal spacing between fractures, and permits the perforation of portions of the interval between fractures. Furthermore, it allows the juxtaposition of any number of perforated intervals and any number of fractures.
The pseudo-steady state is considered to account for the fluid transfer between the matrix blocks and the fracture network.
Due to its simplicity, accuracy, and reliability, procedures for using the new technique referred to as "Tiab's Direct Synthesis" have been developed to analyze the transient pressure and pressure derivative behavior of a MFHW in a naturally fractured reservoir. Individual fracture properties can be determined if individual flow rate contributions are measured, otherwise an average conductivity and half-length is determined.
Introduction
Stimulation of a horizontal well in a low-permeability reservoir may significantly increase the well productivity. Unlike a vertical well, a horizontal well may be fractured at more than one point along the well length.
Yost et. al.[1] presented a case study of a multiply fractured horizontal well intersecting natural fissures. They presented a practical view of the fracturing treatment of a horizontal well in a naturally fractured reservoir. They reported improvement ratios six days after fracturing ranging form 4 to 35 in different zones along the horizontal wellbore.
Mukherejee and Economides[2] presented a simple procedure to calculate the optimum number of orthogonal transverse fractures in horizontal wells and their sizes
Soliman et. al.[3] investigated the pressure-transient behavior of horizontal well with production taking place through finite-conductivity vertical fractures. For transverse circular fracture they obtained a Laplace space solution valid for the period when flow in the reservoir can be treated as linear (towards the fracture plane). Among other things, they compared the effectiveness of finite-conductivity vertical fractures intercepting horizontal and vertical wellbore. Their comparison is valid for short flowing times.
Conlin et al.[4] presented a case study of a multiply fractured horizontal well drilled in a low-permeability chalk reservoir producing under solution gas drive.
Larsen and Heger[5] introduced methods to generate synthetic pressure transient data for MFHW their discussion was restricted to individual or pairs of fractures in unbounded reservoirs in all directions.
Roberts et. al.[6] studied the effect of non-Darcy flow within the hydraulic fractures on horizontal well productivity in tight gas reservoirs. Raghavan et. al.[7] introduced a new model to compute the pressure transient data of MFHWs. They discussed, also, the long time performance of such a completion.
Larsen and Heger[8] presented a comprehensive discussion of the flow periods exhibited by single- and MFHW. They assumed circular fractures. Later on[9] , they presented methods to determine the productivity of such a completion.
Hegre[10] presented a detailed discussion of the simulation of MFHWs. He investigated the effect of both grid cell size and fracture conductivity the have on the transient pressure behavior.
