Results Of Field Use Of Very Low Water Loss Oil Well Cements For Better Producing Capability Of Oil And Gas Wells
Authors: Records L.R. , Ritter J.E. 
Published: December 2007

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
The use of a very low water loss cement to minimize formation damage began in 1975 with efforts to produce a practical oil field cement having an API water loss below 25 cc in a 30-minute test. The theory was that cement filtrates entered formations and damaged them by cementation, chemical deposition, viscosity blockage or chemical reactions causing crystalline growth within the producing formation. Obviously, the smaller quantity producing formation. Obviously, the smaller quantity of cement filtrate available to enter producing formations, the smaller the potential damage. Field results on approximately 30 wells appear to confirm the theory.

Introduction
The Washington Field in St. Landry Parish, Louisiana, was drilled in the 1950's and had a virgin gas pressure of 4589 psi. The field was cycled and the gas sold until the reservoir pressure was depleted to 545 psi on April 21, 1975. pressure was depleted to 545 psi on April 21, 1975. At this point the field was converted to a gas storage project by the Transcontinental Gas Pipeline Corporation. There were 15 original wells in Pipeline Corporation. There were 15 original wells in the field, and it was calculated that 59 more wells would be needed to assure a delivery of 800 MMCF per day during the winter months. It turned out that 28 wells were a sufficient number of wells to do the job.
During the drilling of these wells, it was concluded that special precautions must be taken to prevent entry of mud, cement and preflush filtrates prevent entry of mud, cement and preflush filtrates into the formation where they might block off the permeability of the sand. Any limitation of the permeability of the sand. Any limitation of the productive capacity of the gas storage wells, productive capacity of the gas storage wells, either during gas injection or production, could cause the drilling of extra wells or limit severely the usefulness of the reservoir as a gas storage system.

OBJECTIVES
The Cockfield "D" sand had to be absolutely sealed off so that no leakage could occur from the reservoir during the life of the gas storage project. The seal between "D" sand and other sands project. The seal between "D" sand and other sands in the well had to occur on the primary cement job to prevent micro-annulus leakage.
All of the new wells were to be directionally drilled, and it was thought that reciprocation or rotation of the production casing during the cementing operation would not be practical. Proper cementing had to occur without these general operating practices.
High productive and injection rates of gas movement into and out of the reservoir were necessary to have a successful economic venture. Formation damage had to be prevented during the cementing operations.
Thus, the placement of the cement was of the highest priority if the above objectives were to be met. These were the reasons that cementing companies were asked to design and produce a cement with a very low water loss in the range of 20 cc.

CEMENT SLURRY
The cement slurry was designed to maintain desirable slurry properties of weight, setting time and compressive strengths, and to provide (1) minimum loss of filtrate to the formation, (2) uniform set cement without high water separation as the free water (ranged from 0.0 percent to 0.5 percent), and (3) minimum slurry dehydration with no bridging in the annulus. Potassium chloride was used in the slurry to improve bonding to shale sections, improve bonding in general based on linear expansion properties and to provide a filtrate that would properties and to provide a filtrate that would provide reduced damage from formation clay provide reduced damage from formation clay swelling. Potassium chloride concentrations varied from 10 percent to 25 percent, depending on the available Class "H" cement characteristics.
Compressive strength tests were conducted with the cement slurry and the lime base drilling mud to determine the slurry's tolerance to mud contamination. The results (Table 1) indicated that the slurry could tolerate from 5 to 10 percent contamination by volume without a drastic reduction in compressive strength of the set cement.