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The importance of controlled fluid loss, free water and proper blending of additives for successful primary cementing has been well documented by several authors. In those studies only cement bond logs were used to indicate improvement or failures in the cement job.
This paper will show improved results and monetary savings using controlled cement slurry properties and incorporating good field practices, including the use of spacers, controlled displacement rates, proper centralization, casing movement, and close monitoring of the blending of the cement. This monitoring of slurry properties and field practices will be referred to as a cement quality control program.
This study concentrates on eight Chevron operated onshore and offshore fields in southern California. In this division approximately 135 wells with over 180 casing strings were analyzed. These wells range in depth from 2,000 (610m) to 14,000 (4270m) feet and were drilled from 1980 to the present. Two-thirds of the wells were drilled prior to initiation of the cement quality control program which began in August of 1985.
In the past 15 years, many advances have been made in oilwell cement formulations and application technology. Recent cement technology within Chevron has been directed toward a strong Quality Assurance program. The success of this quality control program is evaluated using remedial cementing costs as its main measuring stick. The remedial cementing costs include direct cementing charges, rig costs, and all associated costs incurred preforming the squeeze job until the squeeze is tested. A second gauge of success is primary cementing efficiency which is defined as whether or not a casing string is squeezed. The efficiency calculation is restricted to intermediate and production casing strings. The results will show that, in these eight fields, (Figure 1) remedial cementing costs have decreased by several million dollars and primary cementing efficiency has risen from under 35 percent to over 80 percent since initiation of the quality control program.
Cement Quality Control Program
The division, from 1980 to 1985, performed 440 isolation squeezes on 116 wells for an efficiency of 34.5 percent. These numbers led to numerous supplemental authorization for expenditures (AFEs) written using remedial squeeze work for justification. A decision was made to reduce this cost and improve all cement jobs. The goal of the quality control program is to bring cementing efficiency to 100 percent and cut expenditures.A Drilling Fluid Engineer position was established to coordinate this program. The initial thrust of the project was to identify cementing problems and then gather all documented or suspected successful cementing techniques to solve these problems. This was a combined effort between the Drilling Superintendents, Engineers and the Cementing Services Section at Chevron’s Drilling Technology Center. These efforts formed the design philosophy. It was the charge of the Drilling Fluid Engineer to monitor, maintain, record, change and implement these techniques when necessary.
This paper shows improved results and savings from a quality-control program that emphasized controlled cement slurry propertis and good field practices, including the use of spacers, controlled displacement rates, proper centralization, casing movement, and close monitoring of the cement blending. This study focuses on eight onshore and offshore fields in Southern California. Roughly 135 wells with more than 180 casing strings were analyzed. These wells, drilled from 1980 to the present, range in depth from 2,000 to 14,000 ft [610 to 4270 m]. present, range in depth from 2,000 to 14,000 ft [610 to 4270 m]. Two-thirds of the wells were drilled before the cement quality-control program was initiated in Aug. 1985. program was initiated in Aug. 1985. Introduction
In the past 15 years, many advances have been made in oilwell cement formulations and application technology. Recent cement technology has been directed toward a strong quality-assurance program. The success of this program is evaluated by comparisons of remedial-cementing costs, which include direct cementing charges, rig costs, and all associated costs incurred during the squeeze job until the squeeze is tested. Another gauge of success is primarycementing efficiency, defined as whether or not a casing string is. primarycementing efficiency, defined as whether or not a casing string is. squeezed. The efficiency calculation is restricted to intermediate and production casing strings.
Results show that remedial-cementing costs have decreased in these eight fields by several million dollars and primary-cementing efficiency has risen from less than 35 % to more than 80 % since the quality-control program was initiated.
The first question raised by a review of the results is whether the reduction in squeeze jobs is the result of improved bonding or a change in completion philosophy. A cement bond log (CBL), run on all production casing strings, was the basis for the determiniation to squeeze. A Log Analysis Division coordinated review of all CBL's to ensure consistent interpretation of the logs. Therefore, any reduction in remedial-cementing costs was the result of improved cement integrity.
Cement Quality-Control Program
From 1980 to 1985, the division performed 440 isolation squeezes on 116 wells for an efficiency of 34.5%. These numbers led to numerous supplemental authorizations for expenditures with remedial squeeze work used as justification. The decision to reduce this cost and to improve all cement jobs was made. The result was a cement quality-control program whose goals were to increase cementing efficiency to 100% and to cut expenditures.
A drilling-fluids engineer position was established to coordinate this program. The initial thrust of the project was to identify cementing problems and then to gather all documented or suspected successful cementing techniques to solve these problems. This was a combined effort between drilling superintendents, engineers, and personnel in the Cementing Services Section at Chevron U.S.A. personnel in the Cementing Services Section at Chevron U.S.A. Inc.'s Drilling Technology Center. The charge of the drilling-fluids engineer was to monitor, maintain, record, change, and implement techniques when necessary.
Abstract Production sections of Western Siberian wells consist of gas, oil, and water-saturated sandstones; therefore, it is extremely important to help ensure zonal isolation to help prevent fluid migration from the overlaid water and gas formations into the oil-producing zones. Isolating the water and gas zones with conventional cement has not been a complete success because fluid migration was experienced through a channel or damage to the cement sheath. A typical solution sets an annular packer in the production casing zone beneath the gas and water-bearing sandstones as backup if the cement fails to provide a full annular barrier. Using the annular packer has some limitations, and potential risks of early activation or nonactivation of the annular packer often contributes to nonproductive time (NPT). An alternative solution used in Western Siberia combines resin-polymer and cement, which provides a cement sheath with improved mechanical properties, such as reduced permeability, increased ductility, and improved shear bond to casing. The successful use of a resin-polymer cement blend as an alternative to using an annular packer, advantages of using this system, and recommendations for implementing this technology are discussed.
Summary The largest discovery of oil and gas in recent years is situated in the Volga-Ural field in Orenburg Oblast. The field was discovered in 2005. The development target is the Devonian Dkt formation which is an aggregate of ancient strata in the Earth's crust that were formed during the Devonian Period of the Paleozoic Era. The Devonian System is divided into a Lower, Middle and Upper series. It consists of alternating layers of sandstone-claystones and siltstones, which have low permeability. Hydraulic fracturing is required to obtain hydrocarbon inflow from this type of rock. The well design employed in the Volga-Ural field incorporates five casing strings and the main challenge while drilling wells in this field is lost circulation. This ranges from partial fluid loss to no returns and has a significant impact on the cementation of the 178/146 mm production casing. Lost circulation has resulted in a failure to achieve the targeted top of cement, annular pressure, annular crossflows and a poor cement bond with both the casing and formation. Prior to 2015, a stage cementing collar (SCC) technique was used to cement the production casing without losses. However, this cementing technique often resulted in poor zonal isolation resulting in water flows between zones. Additionally, after well completion, poor cement bonding to both the casing string and producing formation created a pathway for annular flow of the formation fluids. These challenges called for an alternate solution. This paper presents how foamed cementing technology was used to solve the challenges in isolation of the sandstones and the subsequent improvement of the cementing bond quality. The foam cementing technique was tested in the Volga-Ural field at the end of 2015 and in early 2016 and became the standard solution for cementing the 178/146 mm production.