Delaware Basin Cementing - Problems and Solutions

Abstract

Abstract Increasing drilling activity in the ultra deep horizons of the Delaware basin has focused intense interest on developing effective cementing practices for the problems encountered in this area. Probably the most critical decision facing the drilling engineer is proper selection of casing points to cope with the alternating lost circulation and high pressure gas zones common to the basin. Although the lithology of different areas in the basin is very similar, important differences do exist, and must be recognized to effectively cement these casing strings. The use of formation fracture gradients as an index of design limits has proven to be one of the most effective ways of anticipating the changes required in cementing programs. Gradient profiles of several fields are listed to illustrate the different cementing designs required by seemingly minor changes in lithology. Correct determination and tabulation of gradient profiles has been a significant factor in designing cement placements throughout this area. In general, cementing practice has been influenced by four predominant problems: attempting to cement long annular spaces across weak, incompetent formations; high pressure gas zones that can be drilled with light muds due to limited permeability but are not under complete control during cementing; wide temperature differences between top and bottom of long cement columns; and extremely long liners set in small hole across weak formations. The design of cementing programs to cope with these problems has been an interesting and informative evolution that is followed from the first few wells through present practice. Introduction Probably the most important decision facing the drilling engineer on Delaware basin wells is the selection of casing points. When casing points have been chosen, the next problem is designing an effective cementing program. An accurate analysis of existing hole conditions and correspondingly correct cement design are imperative for successful drilling operations. Making these analyses and correctly predicting cement slurry behavior have been significant factors in reducing drilling costs. Development of the data and analytical techniques to provide this control has been interesting. The first wells drilled in the basin were cemented largely by techniques and procedures used in other fields. Most of the mud weights used were too light to provide an index of cement density limits. Analysis of the results indicated that changes should be made in cementing the succeeding well. This approach is effective, although expensive, in a given field and will finally progress to a successful cementing program so long as formation conditions remain constant. Unfortunately, formation conditions in the Delaware basin are not known for their consistency. Although lithology appears very similar in many wells throughout the basin, important differences do exist. Recognizing and interpreting the effect of these formation changes have determined the success of cementing design in this area. History The first wells drilled in the Delaware basin employed casing programs different from those presently used. A brief resume of these earlier programs will illustrate the importance of selecting effective casing points. Surface casing was set through the fresh-water beds and Rustler dolomite. Intermediate casing was set just above the Delaware sand, covering shale, salt and anhydrite sections. The second intermediate casing was set through the Delaware members and Bone Spring into the top of the Wolfcamp. Another string was required when the Mississippian was topped to shut off Wolfcamp and Pennsylvanian gas. In the Rojo Caballos field casing had to be set just above the Penn and again immediately below it.1 Drilling was then continued to the top of the Ellenburger where another string was set. After the Ellenburger was drilled to total depth, a production liner was set or the well completed open hole. These programs required five strings of casing and six if a production liner was set. Cementing these casings presented problems, but probably not so severe as those in recent practice. Open intervals were shorter and formation extremes were not so wide. Sections prone to lost circulation were drilled and casing set or gas producing zones were isolated, so these two types of formations were not drilled together in one casing interval.