Should Horizontal Sections be Cemented and how to Maximize Value

Abstract

Development of marginal fields offers unique challenges during drilling, completion, stimulation, and production. The underlying objective should be to maximize the value of the field over its productive lifetime. Every phase of the well construction needs to be fully evaluated for subsequent impact on the safety and economics of producing oil and gas from the field. Log evaluation of formation type, thickness, and characteristics may determine the final completion plan, although lack of natural barriers from close water contact may be of major concern when a large stimulation program is required. Specialized low-density cementing systems may be necessary for maintaining satisfactory equivalent circulating density (ECD) for coverage across weak formations. These low-density systems can be prepared either by an engineered foaming operation or by the use of specialized additives blended with cement to lower the density, but production quality properties should be maintained. Consideration should also be given to the final cement sheath properties, which can provide isolation for the "life of well" following cyclic pressure loading from stimulation, testing, and flowing phases. This paper addresses the advantages and disadvantages of the historical approach to constructing and producing horizontals. Completion processes and procedures with emphasis on cementation designs and best practices for horizontal casing are presented with major focus on resulting production rates. These case histories will cover both cemented and uncemented producing wells. Also included will be new methods for predicting cement failure modes as a result of cyclic pressure loading from stimulation jobs. Recent design procedures and ensuing effect for maximum value of the producing asset for life of the field will be compared with historical procedures. Introduction As industry drilling and completion activity increases in the horizontal play of such prospects as the Barnett Shale, many completion techniques will be investigated to determine optimum production performance of the existing wellbore. An important aspect that should be considered is the role of cementation of the lateral section and design considerations relative to execution of this operation. Factors to consider for cementing operations are close water proximity, containment of fracture pressure within treating interval as related to fracture volume size, and number of stages to be performed. Reduced formation pore pressure caused by early depletion of the reservoir should be of concern also in the development stages of well production. Past investigation of horizontal cementing has identified some critical factors necessary for obtaining a successful primary cement job. During the drilling phase of the wellbore, solids settling from the drilling fluid along the low side of the hole can cause mud channels that can be difficult to remove.1 If not removed before cementing, interzonal flow could later be formed, which may jeopardize the production results because of poor zonal isolation. Besides the difficulty associated with displacing low-side solids, the high side of the hole could be susceptible to free water breakout if the cement slurry is not properly designed and tested in the laboratory and mixed on location. A channel formed from free fluid could result in a primary cement failure. This possibility is especially likely in high-angle/horizontal wellbores. Final slurry properties, with particularly close attention paid to free-fluid testing, should result in high-quality cement slurry with long-term isolation characteristics. Particular emphasis on free-fluid testing is found in a later section.