Abstract

Placement of a fracture in a formation has become a well-understood process in the industry. Recently, this practice was improved by the introduction of a method to properly initiate the fracture into a specific direction using super-high-energy jetting. A drawback of this jetting method though is not knowing exactly where the far-field fracture has gone. Although we know that the fracture will extend in the local minimum-stress direction, it is not known where that direction might be. In all probability, the fracture has gone into a less-than-desired area in the formation, and will result in only an "acceptable" improvement of production.

It was once thought that refracturing merely reopened existing fractures. Recently, however, it has been shown that refracturing can actually create new fractures. In addition, when refracturing causes older fractures to reopen, the results generally show that some new area has been reached by the fracture. It is the opinion of this paper that these new areas are not substantially different from the one reached by the first fracture because local depletion enhances the effects of the original stress regime.

This paper discusses a process whereby fractures are generated in a formation using at least two different fracturing techniques to reach formations in a manner not reached by conventional fracturing alone. In this process, the first fracture may achieve "acceptable" production goals, although the cost may be high. A second fracture is then quickly created to take advantage of the stress modification resulting from the first fracture. This rapid followup fracture is thus able to reach more productive rock not accessible to the initial fracture. Field data supporting the feasibility of this concept will be presented. Various situations where this approach could reap substantial benefits are also described.

Introduction

Fracture stimulation has always been an art, mastered by many, and practiced by frac engineers worldwide; and yet, the mystery of mother earth prevails, with its unending surprises in the behavior of the formations below, challenging scientists and engineers continuously and mercilessly. As theories rampantly develop, the question always remains: where exactly did the fracture go? Or, what is the precise shape and measurement of the fracture? The fact is, due to the lack of homogeneity of the formation, precise solutions cannot exist. Obviously, this should not discourage anyone from finding the closest, best solution. It is generally agreed, however, that accurate shape and size are probably not considered as important as the determination of the true direction of the fracture and its reach into the reservoir. Important information relating to fracture reach, for example, would be whether or not the fracture might extend into a water zone or gas cap.

This paper is directed toward the determination of fracture direction and the manipulation thereof. In the literature on this subject, many authors, including this author, have attempted to determine the true direction of fractures through the use of accurate measurement devices, experience, and even geological data.1–4 It is the author's belief that understanding of geological activities provides the best prediction of fracture direction in a formation. Combined with knowledge about formation pressures, this data could be used to determine the frac direction accurately.

However, it is not the intent of this paper to better understand the geological mechanisms that drive natural fracture direction in a formation to determine the direction of man-made fractures. Rather, this paper seeks to find a means for utilizing these natural phenomena to our favor; in particular, in ways that could improve production. The understanding of applicable stimulation processes for this very particular purpose will be discussed.

Hydrajet-Based Fracturing

Because this technology has been described many times,5–7 this paper will not discuss it in depth. Unlike other techniques, hydrajet fracturing does not use conventional packers or bridge plugs, instead it uses dynamic isolation to "seal" flow into specific frac locations. Therefore, as mentioned earlier, this method can treat openhole, preperforated liners very effectively. It has even been used effectively in multilateral wellbores.8–11

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