Multiple, Vertical Fractures From an Inclined Wellbore - A Field Experiment
Authors: Strubhar M.K. , Fitch J.L. , Glenn E.E. 
Published: December 2007

Multiple, vertical fractures can be created from a single, directionally drilled wellbore. The procedure increases the attainable fracture area without adding wells, and provides more rapid and efficient drainage of a specific reservoir volume.

Introduction

For any reservoir with a given set of conditions there should be a drilling, completion, and production procedure that will optimize the financial recovery from procedure that will optimize the financial recovery from that reservoir. This paper focuses on a procedure that should be considered for application in certain types of reservoirs. This procedure involves creating multiple, vertical fractures from an inclined wellbore and the subsequent production from the system.

The effectiveness of hydraulic fracturing is well known, both from experience and from theoretical considerations. The concept of a fracture represented by an enlarged wellbore is discussed by Prats et al. The effects of fracture penetration and fracture conductivity on improvements in production are shown by McGuire and Sikora and Tinsley el al. In low-permeability reservoirs, sufficient conductivity contrast between fracture and formation can be obtained to make well productivity increase almost directly proportional to fracture length. Thus, for vertical proportional to fracture length. Thus, for vertical fractures of fixed height, productivity increase is directly proportional to fracture area.

From the above discussion we can conclude that a method to increase the effective fracture area attainable is desirable. To be useful, any such method must, of course, be more profitable than the practical alternatives.

For a reservoir volume element of fixed size, the maximum vertical fracture area is attained when the fracture is extended to the boundaries of the element. Additional fracture area can only be obtained by drilling and completing additional wells within the volume element. A procedure for producing several vertical fractures from a single well would increase the attainable fracture area without adding wells. Such a procedure and a field experiment to test it are presented here. presented here. The Multifrac Concept

The object of this multiple fracturing process (multifrac) is to obtain greater fracture area through closer fracture spacing than could be obtained from the same number of wells with single, vertical fractures. The increase in well productivity resulting from this greater fracture area per well is not gained without penalty. Because the process requires substantial penalty. Because the process requires substantial deviation of the wells from vertical, both measured well depth and drilling cost per foot are increased when compared with a vertical well. This idea has also been suggested by Pasini and Overby.

The concept is illustrated in Figs. 1 and 2. Theory predicts, and observation confirms, that hydraulically predicts, and observation confirms, that hydraulically induced fractures are generally vertical, except in relatively shallow formations. Thus, it should be possible to generate several fractures from a single possible to generate several fractures from a single deviated hole, as shown in the figures. To accomplish this, the azimuth of the deviated wells must be at a high angle (preferably 94) to the fracture azimuth. The Borehole Televiewer (BHTV) is effective for determining the azimuthal orientation of vertical fractures in a vertical wellbore.

JPT

P. 641