Completion And Evaluation Of Cased Horizontal Wells
Authors: Peach S.C. , Jensen R.E. , Robertshaw S.E. 
Published: March 2010

Horizontal wells in North America have proven to be more economically successful than vertical wells in many reservoir because they can demonstrate several times the productivity of conventional vertical wells(1). New technologies in well design, formation, cement and production evaluation, and perforation of horizontal wells have been developed to help optimize these higher productivities. This paper reviews the utilization and engineered integration of these technologies. A commentary on each includes specific technical and procedural considerations with reference to a recent cased horizontal well completion, Mobil Rainbow 1-14KR-110-6W6.

Introduction

The application of horizontal wells to the production of hydrocarbons from layered reservoirs or reservoirs with thin remaining oil banks, coning problems, or heterogeneity concerns is currently one of the major development areas in petroleum production technology(1). This paper provides an overview of engineering advancements in the areas of wellbore geometry consideration, reservoir evaluation, cement evaluation, perforating design, and production evaluation of horizontal well completions. Technical considerations with supporting log examples demonstrate the utilization and integration of the technologies used to maximize the objectives of horizontal wells. These objectives typically include minimizing drawdown, avoiding high risk intervals, selective completion, and optimizing ultimate productivity and economic recovery.

Wellbore Geometry Considerations

Horizontal well geometry must be fully understood when appraising options for evaluation and completion. Considerations for the following must be made: adequate turning radius for downhole tools and perforating guns, the position of liner top, solids deposition in the borehole, zone isolation, well control, and the irretrievability of equipment run in the well. In addition, deviation data must be examined to establish the limits for wire-line, coiled tubing and drill-pipe conveyed logging operations.

Build rate and casing data are reviewed to determine the maximum rigid tool length and the placement of knuckle joints in the tool string to prevent the string from becoming jammed in the build section. Charts for standard sizes of logging tools and casings have been developed for this purpose. Figure 1 shows that with a maximum build rate of 15 degrees for 30 m, and a difference between the Inside Diameter (ID) of the liner and the Outside Diameter (OD) of the tool string of 75 mm, this well has a maximum rigid tool length criterion of 8 m.

Three different procedures are currently being utilized to convey logging tools through horizontal well sections: tubing or drill-pipe conveyed, pump-down through tubing or drill-pipe, and coiled tubing conveyed techniques.

Tubing and drill-pipe conveyed or pump-down techniques are employed when the horizontal section is too long or hole conditions prevent the use of a coiled tubing conveyed system. The first is performed by pushing the logging tools downhole on the end of drillpipe (or tubing) and a side door sub-routes logging cable from the outside to the inside of the pipe string. Logging is performed by moving the pipe with the rig. The pumpdown system hydraulically pushes logging tools down through pipe or tubing already in the hole, and subsequent logging through pipe is performed by drawing up on the logging cable.