Hydraulic fracturing operations in West Africa are not as common as in the US, Latin America and the Middle East. In the Republic of Congo fracturing technology is spreading and has overcome more than few difficulties since the practice began. The most significant challenge has been the formation, which has shown through laboratory testing to be soft and watersensitive. The fracturing project started in the laboratories, identifying critical issues, such as formation heterogeneity, hardness, water sensitivity, clay content and particularly the risk of proppant embedment. The fracturing fluid chosen for the project was a water-based, borate-crosslinked guar fluid, with specific chemicals added to minimize formation softening and clay swelling issues. A specific pumping strategy was implemented when using waterbased fracturing fluid to limit the effects of proppant embedment. Several wells were treated with this system. In an effort to improve well productivity, a pilot test was designed with oil-based fracturing fluid. This fluid was pumped in two wells, resulting in improvements in terms of cleanup time and economics, compared to the water-based treatment fluids in the same field. Part of the economic benefit was gained because of the reduced hydrostatic head of the oil-based fracturing fluid, which eliminated the need for a coiled tubing gas lifting operation. Economics were also improved by minimizing rentals of well cleanup equipment because the broken fracturing fluid can be sent directly to production facilities. In this paper, design and application results for the oil-based fracturing fluid operations are presented with all the operational and logistical challenges overcome.
Fracture stimulation has been adopted as an integral part of the completion in the M'Boundi field given the results achieved in enhancing well productivity, as well as the positive impact realized on field development economics. The fracturing process has been optimized over the years through improved reservoir understanding and ensuing implementation of technologies to address the uncovered challenges. Changes to the fracturing fluid formulation to prevent damaging the water sensitive reservoir rock, as well as modified proppant schedules to mitigate proppant embedment are examples of this improvement process. This paper describes the successful ongoing process of optimizing hydraulic fracturing designs in M'Boundi field. By applying an integrated approach combining various technologies, it was possible to better understand fracture propagation and coverage of the target reservoir. Implementation of a novel non-radioactive traceable proppant allowed accurate frac height measurement at the wellbore. When combined with rocks mechanics derived from sonic logs it led to redefining the mechanical earth model and ultimately the completion and fracturing strategy in the field. The process will be illustrated with examples from a 3-well campaign recently executed onshore Congo.
Water and gas management in mature fields is a daily challenge. It is even more critical when re-development is required using existing assets to be side tracked. The severe depletion of the oil zones creates significant pressure contrast with water and gas layers that need to be properly isolated. Failure to correctly cement the casings or liners generally ends up by generating cross flows, not only affecting the current well but also other wells producing from same levels. The paper is based on a successful case history, performed in Congo for a major, where the restoration of the zonal isolation on highly deviated wells was required. The objective of the paper is to describe the methodology process to determine the source of water in a well, the merge of oil field competencies to engineer a chemical and mechanic solution, the fluid design and the full operational deployment on location to cure the problem. The combination of several specialties provided an innovative solution that gave the following benefits: -Minimize the number of runs, with only two trips required to perforate the liner to access the cross flow area and to set a straddle assembly-Minimize well restrictions and still give access to the lower completion-Minimize risks of getting stuck using sealant polymer instead of cement-Provide complete annular isolation and restore casing integrity in a same run-Evaluation and control of the cross flow before sealing operation-Protect the lower oil producing zone during the entire remedial operation At the end, the objective of the paper is to give best practices to perform remedial cement operations in similar well architectures.
When designing a hydraulic fracturing intervention, the selection of the interval to be perforated is critical in order to maximize oil production and to avoid unwanted gas/water breakthrough from neighboring layers.While on new wells the perforation interval can be selected carefully analyzing logs and CBL, it can be challenging to design a workover where the HF targets a zone that is right in the middle of a large existing perforated interval (125 meters).Leaving exposed too many perforations during a fracturing treatment could result in operational issues such as early screenout and/or uncertainties on the fracture initiation point. Zonal isolation could be obtained by cementing part of the perforations but this would mean in permanently losing part of the level. This paper will describe a successful workover carried on a shut-in oil well, onshore Congo, where a single stage fracturing treatment was performed leaving exposed only few meters of the existing perforations and without permanently losing the remaining intervals.This result was obtained using a multi-stage ball drop frac completion setting the packers across the perforated interval. The downhole equipment was able to withstand the treating pressure during the fracturing treatment and production was obtained through the frac sleeves.This workover resulted in a significant oil production from a well that never produced until that moment.
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