Abstract

CL Consultants Limited has been involved in over seventy horizontal wells in S. E> Saskatchewan. From this experience has arisen a number of observations as to the tolls and skills needed in geosteering and the determination of reservoir quality. The mandate of the wellsite geologist is to place and maintain the wellbored in an predetermined location deemed as optimum. Samples, hydrocarbon detection, survery data, and LWD tools are constantly providing information to the wellsite geologist. How the geologist in the field uses this information to steer the bit to and within the reservoir and make determinations as to reservoir quality will be discussed.

Introduction

In 1989 CL Consultants was contracted to provide the Hydrocarbon Logging and the Wellsite geologist for a well in central Alberta. This project was to drill the Nisku horizontally. The depth of the zone was clearly outlined and a predetermined depth to go horizontally was defined Using the hydrocarbon logging equipment in particular the chromatograph, an oil contact was identified. Once this contact was reached it was clear what depth had to be maintained in the horizontal leg. The well proved to be very successful and upon completion of the job many observations were made and many questions where raised Correlation of the samples and the hydrocarbon data to the wireline data was very concise Porosity and reservoir quality could be defined while drilling. This, combined with the ability to steer the bit into the best reservoir made the proposition of horizontal drilling very exciting.

Today, the skills tools and knowledge have greatly increased. With this expansion this techniques, the responsibilities of the well site geologist have changed and expanded. On a typical vertical well one geologist is responsible for tracking the wellbore as it drills through the various strata to a generally predetermined total depth Samples penetration rate and hydrocarbon detection provide many clues to that is occurring down hole. Once the primary objective is drilled the Geologist reports observations on porosity, fluorescence, and other hydrocarbon evidence The zone is then logged and all the information is compiled and the fate of the well is determined. Reservoir quality is based primarily on the open hole logs.

The role of the geologist in a horizontal application creates an entirely different operational situation on the location. The entire process starts with the project geologist Interpreting the final is the most optimum location for the wellbore in the reservoir. Prior to drilling this "best spot" is outlined to the wellsite geologist in the form of a window that must be maintained. Once the wellsite geologist is on local on the build section has to be monitored and the correlation of the over lying strata must be carefully followed to ensure the reservoir is coming in according to the prognosis. Any changes in the build section are discussed with the project geologist to see if any angle changes to the build are required. Once the reservoir is encountered the window is maintained. If the rock changes a change in wellbore trajectory is necessary.

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