Abstract Laboratory experiments had been carried out by using G and special blended cement with various amount and types of standard cement additives, and various amount of local bentonite and sugar cane fiber. The ASTM-C 114 and AAS procedures were used for the chemical analysis and API Spec. 10 procedures under atmospheric and reservoir conditions for the cement performance.
One of the serious cementing problems is a lost circulation, which may occur in high permeability formation, vugs or naturally fractured formation. Therefore this study focused on development of a cement mixture to overcome lost circulation problem and also strong enough to hold casing with minimize damage to potential producing formation. The results shown that optimum size of local bentonite ranging from 150–250µm and sugar cane fiber ranging from 2000–2800µm. A suitable cement system formulation for optimum lost circulation control is 9% local bentonite, 2% calcium chloride, and 0.5 sugar cane fiber with adequate shear bonding strength and formation permeability reduction is about 10%.
Generally, special blended cement has less free water and fluid loss, better strength development but shorter thickening time than G cement. The cost of blended cement is cheap, bentonite is a local material and sugar cane fiber is a waste material, therefore there will be about 48% of the cement material cost saving if this cement formulation is used for an average oil well at 8,000 ft depth. This formulation also proves to be the cheaper choice for cementing job, particularly the shallow well due to the shorter thickening time.
Introduction Cementing job is the process of placing cement slurry to the desired location in the annular between casing and well bore with general functions to bond the casing and formation, to protect producing strata, to prevent the migration of formation fluids between zones, and to control lost circulation. Lost circulation is a concerned problem for many years. Many previous works have used materials such as mica, cellophane, walnut hulls, foamed cement, and high strength micro sphere (HSMS) for lost circulation control. However, this type of material may result in permanent damage of producing formation. The target of this study is to develop a cement system that can control lost circulation and not inhibit productive formation.
Experimental work All tests were performed in accordance with API Spec. 10 (1990) at room and simulated reservoir conditions in order to determine the effect of amount and grain size of local bentonite and sugar cane on suitable cement system performance for lost circulation control during fractured formation cementing job. The ASTM-C 114 and AAS procedure were used for chemical analysis of bentonite.
Local bentonite was graded in particle size from 75µm to 850µm with percentage ranging from 3 to 12% by weight of cement (WOC). Sugar cane fiber was graded in particle size from 0.5 mm to 4.75 mm with percentage ranging from 0.5 to 2% by WOC. Calcium chloride concentration used was 2% to 4% WOC.
Results and Discussions Bentonite Composition The XRD analysis results of local bentonite and Wyoming bentonite were shown in Table 1. From the results, it is found that local bentonite only consist of 45.5% montmorilonite and 5 % hematite as compared of 86% for Wyoming bentonite.
Sugar Cane Fiber Composition The fiber compositions in sugar cane stalks contain cellulose, himecellulose and lignin. Therefore, a sugar cane fiber can act as the fluid loss and retarder additives (Shell &Wynn, 1958).
Bentonite Composition The XRD analysis results of local bentonite and Wyoming bentonite were shown in Table 1. From the results, it is found that local bentonite only consist of 45.5% montmorilonite and 5 % hematite as compared of 86% for Wyoming bentonite.
Sugar Cane Fiber Composition The fiber compositions in sugar cane stalks contain cellulose, himecellulose and lignin. Therefore, a sugar cane fiber can act as the fluid loss and retarder additives (Shell &Wynn, 1958).