Oriented Fracturing: A New Technique To Hydraulically Fracture an Openhole Horizontal Well

Abstract

Abstract Successful fracturing treatment necessitates expensive completion assembly that provides some form of isolation to perform controlled fracturing treatments. Currently isolation is performed mechanically which dictates that isolated interval is very short. This in turn may require that the well is cased, cemented and perforated. This would increase the cost of completion significantly. Another option is to focus the fracturing energy via the use of hydrajetting. In this paper we present another approach that provides a high degree of control on where the transverse fractures will initiate and propagate. The various existing techniques for creating multiple hydraulic fractures along an openhole horizontal well are briefly summarized. Laboratory experiments shedding light on some of these techniques will be first presented. The new technique to precisely place a hydraulic fracture in an openhole horizontal well drilled in any direction relative to the in-situ stress field is presented. The new technique is based on rock mechanics understanding of an openhole horizontal well under a given in-situ stress field; thus it accounts for the near wellbore stress field to ensure creating a planar hydraulic fracture. Additionally, the new technique does not require costly mechanical isolation to place a hydraulic fracture. Basically, the new technique aims to bypass the near wellbore stress field such that the fracture can be conveniently initiated independently of the stress direction. This new approach is validated using laboratory experiments which will be discussed in details. The experiments were performed on simulated wells casted in rock samples with dimensions of 6"x 6"x10". The samples were triaxially loaded simulating various arrangements of a given wellbore relative to the in-situ stress field. Then, the simulated wells were hydraulically fractured using water based gel. Fracturing pressure versus time was recorded and analyzed. The experiments were very successful in proving the new concept to fracture openhole horizontal wells. The developed technique is fairly easy to implement and the impact of precise placement of a hydraulic fracture across an openhole horizontal well is illustrated. Introduction Hydraulic fracture stimulations have been commonplace in the hydrocarbon producing industry since the 1950's, when Stanolind Oil company performed the known first fracturing operation using hydraulic pressure.1 Prior to this, well stimulations were done using acid; while fracture stimulations were mostly done using explosives, mainly TNT.2 Obviously, this approach is hazardous especially in today's standards; and the results are unpredictable. During a long period thereafter, wellbores are mostly vertical; and the use of hydraulic fracturing becomes commonplace in the industry for enhancing production of the lesser-than-desired producing wells. The task seems to be simple and consistent enough - pump and reap the benefits. The fact is, that in the average medium depth wells (note - most wells during that era are between 2000–6000 ft) fractures are generally vertical or almost vertical; thus fractures initiated from a vertical well are generally longitudinal relative to the wellbore as shown in Figure 1. Even though perforations are shot in many different directions, there are always a few that will be perfectly aligned with the fracture. As the industry embarks upon horizontal well completions, different problems emerge. As the well goes horizontal, the fracture does not. Since the fracture plane is determined by the local stress field, and the wellbore is determined by design team decisions, the relative position of the fracture to the wellbore is generally unknown. Better understanding of the fracture behavior in horizontal wellbore is therefore needed to provide the best judgment or solutions for fracture stimulating a horizontal or highly deviated wellbores.