Class G Cement in Brazil - A Statistical Approach
- F.C. Rose (Petrobras S.A.) | Osmond Coelho Jr. (Petrobras S.A.) | F.J. Parente (Petrobras S.A.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- September 1993
- Document Type
- Journal Paper
- 179 - 183
- 1993. Society of Petroleum Engineers
- 1.14 Casing and Cementing, 4.1.5 Processing Equipment, 1.6 Drilling Operations, 1.7.5 Well Control, 1.14.4 Cement and Bond Evaluation, 4.2.3 Materials and Corrosion, 5.2 Reservoir Fluid Dynamics, 4.1.2 Separation and Treating, 1.10 Drilling Equipment
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Since 1975, Petrobras has worked with Brazilian Portland cementmanufacturers to develop high-quality Class G cements. The Petrobras R&DCenter has analyzed each batch of Class G cement manufactured by prequalifiedproducers to API Spec. 10 standards and to Brazilian Assoc. of prequalifiedproducers to API Spec. 10 standards and to Brazilian Assoc. of TechnicalStandards (ABNT) NBR 9831 standards. As a consequence, the Drilling Dept. atPetrobras now is supplied by three approved Class G cement factoriesstrategically located in Brazil. This paper statistically analyzes test resultson the basis of physical parameters of these Class G cements over 3 years.Statistical indices are reported to evaluate dispersion of the physicalproperties to obtain a reliability index for each Class G cement.
After manufacturing the first Brazilian Class G cement for nearly 15 years,until 1988, Petrobras, cement service companies, and cement manufacturers haddeveloped uniform batch analysis and approval procedures.
On the basis of the cement manufacturers' experience and the results ofbatch approval tests, the Drilling Dept. Cementing Sector at Petrobras decidedto modify this cement systematically. The Cementing Sector began to analyze andapprove alternative batches from two highly reliable cement manufacturers:batches from a third manufacturer were maintained in this same manner. Thisprocedure was adopted with the goal of analyzing only random batches, fromthese three manufacturers as the quality and reliability of their cementsincreased.
This newly adopted approach was based strictly on the experience andintuition of technicians involved in Class G cement analysis and development,however, and lacked a technical basis. Thus, this paper was written not only totest our theories, but also to improve our knowledge of the quality of threeBrazilian Class G cements.
In 1975, Petrobras began a procedure that culminated in the technologicalqualification of Class G oilwell cement for the Brazilian drilling industry.Obtaining a good Class G cement, uniform not only among batches but also withineach batch, is not easy. It requires accurate technology involving manyvariables, such as rigorous selection and strict dosing of raw material,velocity and temperature control at the rotary furnace, and clinker crushingcriteria.
For cements to reach the present quality level, which has been maintainedsince 1984, both Petrobras and suppliers invested heavily in the development ofhuman resources. Thereafter, the Petrobras Drilling Dept. and Cementing Sectorwith the participation of cement service companies, cement manufacturers, andthe Brazilian Assoc. of Portland Cement (ABCP) began the Brazilian Standards ofCement for Oil Wells project to create quality standards for Class G cement.ABNT approved these standards, and Petrobras adopted them in March 1988.Petrobras adopted them in March 1988. Data Collection
To answer our questions regarding cement quality, we decided to use amathematical treatment reflecting the behavior of Class G cements. Data wereselected on the basis of the standardized physical properties of the threecements Petrobras uses.
We chose to conduct a sampling as soon as possible (assuming that themanufacturers had a well-controlled cement production process) to provide aconsiderable data population that would make true statistical analysispossible. May 1986 through May 1989 was chosen as the data collection possible.May 1986 through May 1989 was chosen as the data collection period on the basisof Class G cement evaluation test results filed with period on the basis ofClass G cement evaluation test results filed with the Petrobras DrillingDept.
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