The production of hydrocarbons from pressure-depleted zones is becoming a common practice around the world and drives the constant development and improvement of cementing technology. This paper addresses the evolution of lightweight cement slurries to ensure zonal isolation and mechanical stability of casing in highly permeable and depleted formations. To prevent lost circulation while cementing depleted formations, a new technique has been developed based on adding inert fibers to ultralightweight slurries. During the cementing operation, the fibers create a network across the loss zone, to enable the cement to bridge off these zones and regain circulation. Also, these fibers enhance the mechanical properties of the cement as the created net provides additional stability to resist tensile stresses. This paper discusses the challenges and solutions of developing ultralightweight slurries (without foaming) that control rheology and cement properties by the interaction of fibers and cement particle size distribution. The paper addresses the synergies that cement slurries and inert fibers, with specific gravity values between 1.0 sg and 0.88 sg, bring to cement production casings in the Cantarell field of Mexico. The pay zone of the Cantarell field is a highly fractured, highly permeable, vuggy, and depleted Cretaceous formation that is typically drilled under total loss of circulation. The ability to reduce and prevent losses of slurry by adding this engineered fiber helps to ensure that the cement slurry is placed according to design to provide good zonal isolation and to permit completion of the new well. Introduction The design of the primary cementing job in the Cantarell field has been a continuous challenge to achieve a good zonal isolation along a Cretaceous formation which is considered the main producing horizon for Mexico in terms of barrels of oil produced per day. Cantarell field (Fig. 1) is the second largest producing field in the world behind Ghawar field in Saudi Arabia and was discovered in 1976. The upper reservoir is an uppermost Cretaceous brecciated dolomite, and the lowest stratigraphic reservoir in the field is a lower Cretaceous dolomitic limestone. The field is made up of a number of subfields or fault blocks, which geologically are in an overthrust structural setting. The subfields are: Akal, Chac, Kutz, and Nohoch. The field reached an early peak in production of 1.1 million B/D in April of 1981 from 40 oil wells; however, in 1994, the production was down to 890,000 B/D. One year later, in 1995, it was producing 1 million B/D because the Mexican government decided to invest in that field to raise the production level. To reach that level, the local operator built 26 new platforms, drilled many new wells, and built the largest nitrogen extraction facility capable of injecting a billion ft3/D of nitrogen to maintain reservoir pressure. Consequently, they were able to raise the oil production rate in 2001 to 2.2 million B/D. Today, the field produces 2.1 million barrels. On the other hand, analysis indicates that the gas located at the upper section of the formation zone will continue to progress in Cantarell as a result of hydrocarbon production. Thus, currently producing wells will stop producing in the future. The pace at which production will decrease will depend on the number of wells that continue to produce. Therefore, included in the stated goals for the project, based on the reservoir management policies, is the maintenance of pressure by injecting nitrogen and the closure of wells with high gas/oil ratio.

IntroductionThe Cantarell oil field in the Gulf of Mexico is located in the Bay of Campeche. It is the largest oil field in the area with an average production of 317,975m 3 /d oil (2 million BOPD) from the Brecha formation. The formation is in the Paleocene and Cretaceous zones with a thickness from 150 m to 900 m (492 ft to 2,953 ft) and greater than 5-µm 2 (5darcy) permeability.After producing for more than 25 years, this field has been depleted. Several years ago, wells were drilled without any returns (total lost circulation) using oil-based drilling fluids with densities as low as 0.88 g/cm 3 (7.3 lbm/gal). These levels do not even reach the surface [1,500 m (4,921 ft)] below the surface] due to their low integrity where the formation pressure gradient is equivalent to 0.55 g/cm 3 (4.6 lbm/gal) and the fracture pressure equivalent to 0.65 g/cm 3 (5.4 lbm/gal). These very low pressure conditions resulted in considering the use of ultralight cement slurries with similar densities to the drilling fluid to bond the production casing during the final stage of the well construction. AbstractIn the oilfield industry, many resources have been allocated to develop lightweight slurries that will reduce the equivalent hydrostatic pressure against low-pressure formations and achieve successful zonal isolation while performing a cementing job. However, to comply with the standard recommended practices for cementing operations, it is crucial to maintain a progressive rheological and density trend from the spacer up to the tail slurry. Centralization and friction pressure play another very important role in achieving a suitable design and have to be considered during the design stage as well.The use of ultralight cement slurries has also created the necessity for the evolution of the spacers used during the cementing operations in terms of density. This paper describes how a lightweight spacer with 0.88 g/cm 3 (7.3 lbm/gal) density was developed and its important contribution while performing a cementing job in a depleted zone.

No abstract