The South Region of PEMEX in Mexico produces 530,000 bopd from mostly mature, naturally-fractured carbonate reservoirs. The majority of the well interventions in the area present complications, due to a combination of extreme operational conditions, variety of reservoir rocks and fluid environments, and complex well configurations required to produce from large intervals in different flow units, many supported by active aquifers and secondary gas caps, that eventually reduce the production of oil as the water production and gas production increase. Rigless stimulation and maintenance well operations have been recognized for decades as efficient and cost-effective production enhancement enablers in the area. As the fields mature and the well interventions become more challenging, there is a higher demand on the operator side to successfully pinpoint the intervals and execute treatments that overcome unknown downhole parameters with confidence, maximizing success and avoiding additional remedial work. A new approach, incorporating real-time, coiled tubing-deployed, fiber optics monitoring, was implemented in three well interventions in southern Mexico. These included: (a) the isolation of a high-water producing interval in a low-pressure reservoir using an inflatable packer; (b) a matrix stimulation requiring the accurate placement of fluids and diversion stages; and (c) the perforation and testing of several intervals in a gas injector well. Real-time down-hole measurements of performance have been found to be an excellent option to improve the success rate in the well interventions in southern Mexico, allowing capturing unique quantitative feedback from the well, to be able to act with a greater degree of precision to increase production. Coiled tubing-deployed fiber optics proved to help the operator to improve efficiency and to optimize intervention performance with confidence in real time.
Xan is Guatemala's largest oil field, accounting for more than 90% of the country's production. Xan produces from a complex dolomite reservoir at average rates of 10,500 BOPD, with most of the production coming from 8 horizontal wells with typical open-hole completion lengths of 1,500 ft. The majority of the horizontal wells at Xan do not produce at their fullest potential because of near wellbore damage, associated to drilling fluid residues, and problems related to the high production of water, averaging 90% water cut at the field level. This paper presents an innovative approach combining diagnostics supported with fiber optics distributed temperature survey data feedback and matrix stimulation systems, tailored to address specific needs, including viscous-highly retarded emulsified acid systems, multifunctional solvents, and surfactant visco-elastic diverting agents, all deployed through coiled tubing to remove the damage and maximize the treatment penetration in the reservoir. The solution was tested in two horizontal wells with severe formation damage and water production problems. The use of coiled-tubing deployed fiber optics facilitated monitoring and evaluating the stimulation treatments and fluids behavior in realtime, by capturing a sequence of temperature profiles and temperature responses to the acid injection at different times through the treatment. As a result, zonal coverage and effectiveness of the stimulation and diversion systems could be quantified as the treatment was pumped; allowing optimization of the stimulation program and pumping variables to accommodate to the actual well's response. Production results have been outstanding, oil production increased by 54% from the two horizontal wells, which is equivalent to the production of a brand-new development well in this field, at a much lower cost. The diagnostics-solution approach developed for this reservoir helped accurately diagnosing the problem and implementing a fit-for-purpose stimulation treatment that actually improved oil production. The proposed methodology has substantially changed the process of stimulating horizontal sections in the Peten basin of Guatemala.
With the discovery of new fields becoming less common and the need to maximize economic recovery in mature fields, operators are trending towards rig-less intervention work to reduce cost and delays to production related to traditional workover rig interventions. With its field complexities, from low bottom hole pressure (BHP) to high temperature/high pressure (HT/HP) reservoirs, and from consolidated sandstone to naturally highly fractured carbonates, and large producing intervals in various flow units with active aquifers, southern Mexico poses a highly significant challenge for rig-less intervention in water control and zonal isolation to assure placement and accuracy of treatment fluids. This paper discusses the implementations and results of two case histories in which a cost-effective application involving coiled tubing and inflatable packer systems were used for water control in a high water cut producing well and for well abandonment of a newly completed well. The utilization of coiled tubing combined with the inflatable packer is able to precisely deliver the treatment fluids to the zone of interest while the production tubing remains in place, which enhances timely and cost effective intervention solutions1 when compared to workover rig operations. Case 1 presents the water control application using a coiled tubing inflatable packer system in combination with an organic crosslinked polymer gel, and micro-fine cement slurry for a naturally fractured carbonate reservoir in southern Mexico. The result of this innovative rig-less approach exceeded the operator's expectations. The case history well was producing 815 BOPD and 5.2 MMSCFD with a water cut of 77%. After the water control treatment with the coiled tubing inflatable packer system, organic crosslinked polymer gel and micro-fine cement slurry, the well was producing 1,459 BOPD and 5.15 MMSCFD with a water cut of 0%. Case 2 demonstrates a newly completed well with production tubing and packer already set and the well producing with high water cut from an open-hole completion. By using the inflatable packer system through coiled tubing and squeezing cement slurry to abandon the open-hole, a new interval could be perforated and exploited in just 28 hours; in contrast, conventional abandonment with a rig can take up to 10 days.
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