New Techniques for Hydraulic Fracturing in the Hassi Messaoud Field

Abstract

Abstract The Hassi Messaoud oilfield is a thick sandstone reservoir in the north-easternpart of central Algeria. The reservoir was discovered in 1956 and produces froma Cambrian-age sandstone at approximately 3400 meters depth. Hydraulicfracturing has been successfully used to improve oil production since 1990. Pre-treatment injection tests have been conducted on approximately 250 wellsand proppant has actually been placed in approximately 200 wells. The 50 wellson which only injection tests were conducted were reviewed. The review showedthat there were three main reasons why treatments were aborted after theinjection tests:mechanical failure of the well,treating pressure toohigh, andfracture geometry, as interpreted from temperature logs, createdoutside target interval. In order to increase the success rate of the treatments two new techniqueswere recently introduced. * Propellant stimulation techniques were used to reduce fracture initiationpressures and to control the fracture initiation point. * A dual fracturing technique was introduced to control downward growth of thecreated fractures. The paper presents three well-documented case histories to illustrate theapplication of these new techniques. The data presented includes pre- andpost-treatment production, peak pressures from the propellant runs, temperatureand radioactive tracer logs from after the injection tests, and radioactivetracer logs that show the actual placement of the proppant. Introduction The Hassi Messaoud oilfield, one of the giant oil fields of the World, is athick sandstone reservoir in the north-eastern part of central Algeria (seeFigure 1). The field was discovered in 1956 and covers an area of approximately 2000 km2. Currently, the field has around 1000 wells. Figures 2 and 3 show amap of the field and a typical cross-section with the different productivehorizons (drains) as found in the field. Hydraulic fracturing has been used asa technique to increase production of the oilfield since the early 1990s. Historic overviews of hydraulic fracturing activities have been presented intechnical papers by McGowen et al. 1 and by Bouazza et al. 2. A significant amount of oil currently produced from the Hassi Messaoud fieldoriginates from wells that were hydraulically fractured. This is illustrated inFigure 4. At the end of 1999 proppant had been placed in approximately 200 wells in the field while injection tests had been conducted on approximately 250 wells. Figure 4 also illustrates that the production starts to decline asthe number of fracturing treatments decreases. The main reason for the decreasein number of treated wells is the difficulty in selecting new candidates forhydraulic fracturing. A review of the results of the 50 wells on which only injection tests wereconducted revealed that were three main reasons for not conducting main treatments.Mechanical failure of the well generally caused unsetting of the anchorseal.Conservative pressure limitations.Fracture geometry, as interpreted from temperature logs, created outsidetarget interval. Propellant stimulation and a dual fracturing technique to better controltreatment placement within target interval, were identified as potential newtechniques to tackle the problems associated with wells in categories 2 and 3. This paper starts with brief summaries of the propellant simulationtechnique and the dual fracturing technique. The next section describes casehistories in three wells in the Hassi Messaoud field in Algeria. The paper endswith discussion of the results and conclusions.