Horizontal Wellbore Placement Can Significantly Impact Hydraulic Fracturing Stimulation Results
Authors: McDaniel Billy W. , Surjaatmadja Jim B. 
Published: December 2007

In addition to rock permeability and reservoir pressure, variables important to the production of lateral wellbores have three major differences from those of vertical wells. These are (1) length of wellbore within the producing zone, (2) gravity effects, and (3) reservoir compartmentalization effects. If a horizontal wellbore will need hydraulic fracture stimulation a fourth variable, in-situ rock stress values and their directions, becomes a major factor:

Historically, stress effects have been considered primarily for borehole stability concerns but become much more important to production potential if hydraulic fracturing is necessary for stimulation.

Before the recent surge of horizontal drilling in ultratight gas reservoirs, only a small percentage of horizontal completions were known to be hydraulic fracturing candidates before drilling the well. Technology advancements have now significantly broadened the industry's ability to effectively place multiple fractures at preselected locations along a lateral section. In recent years, a large number of horizontals drilled in moderate to low-permeability oil and gas zones have proved only marginally economic; many were not economic when in layered reservoirs. For many of these wells, rapid production declines experienced on the "non-candidates" caused them to become stimulation candidates; and only then did the operator realize that many were drilled into a direction that decreased the opportunities for effective stimulation.

Many horizontal wells will eventually need stimulation, even if not at initial completion. Identifying the type of the needed stimulation must be considered before the drilling and completion of the well. When lateral lengths were typically only a few hundred feet there was a higher probability that the formation in-situ stress condition would be essentially constant. As laterals are more commonly being extended thousands of feet, quite often they may be drilled through multiple fault blocks where the stress field can drastically change from one section of the lateral to another. When this occurs, a need to effectively fracture stimulate can result in significant changes to the way a fracturing placement program is implemented at specific locations along the lateral. The desire to "stimulate with the bit" has multiplied the number of multilaterals being drilled; if poor production forces an operator to consider fracture stimulation, this can further emphasize the importance of stress direction vs. lateral direction.

This paper is intended to aid understanding of the ways that lateral wellbore placement and completion plan can influence (improve or reduce) the effectiveness of hydraulic fracturing applications. There is specific emphasis on many of the field and reservoir aspects (such as formation geology and localized tectonics) which may influence proper placement for future applications of fracture stimulation. Some aspects relate to well placement and others to specifics of lateral section locations.

In the final section we will also reference many recent new techniques being applied to control fracture placements along laterals. Discussions include laterals that are completed as a barefoot open hole, with a non-cemented liner (pre-perforated or solid), or as cemented liner completions.