We describe the situation and challenges, the implemented process and strategies, and the downhole tools used during the remedial work to successfully recover 3041 m of 1 3/4-in coiled tubing (CT) pipe lost-in-hole during an acidizing job. During an acidizing job through the CT string as a part of a workover job in a well of a mature field in offshore Mexico, after filling the pipe with acid, the CT operator was ready to spot it across the perforated interval. When the up-hole movement started, the CT weight reached approximately 36,000 lbf (normal pulling weight at that depth in the previous runs) and then the CT weight went to 0 lbf. After retrieving the pipe to surface, it was noticed that only 199 m of CT were recovered from the well, leaving +/- 3041 m of CT pipe inside the hole. After a total of 43 runs and over 20 days, the entire CT string including the Bottomhole assembly (BHA) was recovered, and the well was put back on production. The key was to conform the top of the fish with a downhole motor equipped with a milling shoe, and then exploit the versatility and fast rig up/down capabilities of slikcline to position the fishing tool on the top of the fish. After the fish was latched, a GS profile was left in hole, thus allowing the CT to latch and retrieve the entire fish. Fishing operations are considered more an art than a science because of all the variables involved, for example, type and top of the fish, restrictions along the wellbore, available fishing equipment, pulling capacities, and so on. However, following industry best practices, fishing can switch from a nightmare to a useful learning and successful experience. The authors will summarize the milestones in the operation, which serves as an example of collaborative work between the operator and service company that led to a successful outcome.

The present work reports requalification results of 33 platforms installed in the Bay of Campeche (BOC), Offshore Mexico, based on simplified and detailed ultimate strength analyses. These analyses have been carried out according with the Transitory Criteria (TC) developed for the BOC and the API RP 2A 20th edition. Taking into account that simplified structural analysis performed with a software called Template Offshore Platform Capacity Assessment Tools (TOPCAT) are quick and conservative as compared with sophisticated computer programs, PEMEX - IMP decided to use this software. In general terms, results obtained with TOPCAT agree well with those from the sophisticated software. Introduction As an offshore platforms becomes older it is more difficult to comply with modern codes, due to accumulated damages load increments, changes of service and so on. On the other hand codes are stricter than the ones used in the design of old platforms. A structure that does not comply with a code can not be replaced with a new one, because this implies time and cost, among other technical problems. Fortunately API issued Supplement 1, which is applicable to requalification of existing offshore platforms. As a result of the first non-linear ultimate strength analyses carried out for PEMEX according with Supplement 1, Petroleos Mexicanos (PEMEX) and Instituto Mexicano del Petroleo (IMP) developed the TC for design of new offshore platforms and requalification of existing structures in the BOC. API RP 2A Supplement 1 and the TC change the engineering practices, including the non-linear ultimate strength analysis as a compulsory task when assessing an existing structure that does not pass the design level analysis or does not have adequate deck height. This change requires reliable software for ultimate strength analysis. For planning and taking decisions purposes PEMEX needed some structural assessments in a short period of time, too short to carry out detailed structural analyses. Therefore, TOPCAT was used to assess nine platforms considering that this software gives quick and conservative results as compared with those from sophisticated software. Nine platforms were assessed in one week by a group of three structural engineers. With sophisticated software this nine structures could not be assessed in this time. For this reason and the results obtained with the simplified ultimate strength tools, PEMEX - IMP have carried out several analyses. However, TOPCAT itself can not replace the sophisticated computer programs. Requalification of 33 platforms was conducted, analyses were carried out with simplified and sophisticated tools and results of both tools are very close. TOPCAT has the capability to model damages on the structural members such as dents and out of straightness, as well as the capability to consider grout repair of week members. Based on the above mentioned if necessary one can recommend to grout repair structural members. In some cases, it is recommended to perform detailed analyses, because detailed analysis could be less expensive that grouting members.

Production in mature offshore Mexico fields is mostly driven by gas injected from surface. With time, injected gas flows directly through natural fractures in the low-pressure carbonate reservoirs, leaving oil trapped in the low-permeability matrix and reducing crude production. Over the past few years, the gas-oil contact has rapidly moved across those fields making conventional gas shutoff techniques both unsuccessful and uneconomic. An innovative approach introducing a fit-for-purpose polymer foam system (PFS) and its accurate placement using coiled tubing (CT) real-time telemetry addresses those challenges with an unprecedented success rate while optimizing both logistics and operational time. To selectively shut off unwanted gas in these naturally fractured reservoirs, the PFS was designed to have a high foam quality and low density. Thanks to a delayed crosslinker, this formulation enables deep penetration along the fractures and fissures before the gel strength develops. To ensure effective placement of the PFS and its activation at the right depth, CT downhole gauges monitor pressure and temperature throughout the pumping stages. Any deviation from the downhole schedule can swiftly be addressed to maximize shutoff effectiveness at depth. Monitoring of downhole parameters is not only instrumental to the PFS placement, it is also critical to other services associated with conformance operations. Thanks to the casing collar locator and gamma ray signals, it enables accurate depth control during perforating and stimulation phases. This system also facilitates the evaluation of the wellbore response after each main stage of the intervention. Finally, it can help perforate new intervals with minimum impact to the already pumped conformance treatment through the use of a new perforating firing head whose activation is controlled through fiber optics rather than triggered by hydraulics. The introduction of this methodology in offshore Mexico led to an increased success rate in gas shutoff operations. Of the nine wells that had interventions performed in 2015, eight were initially closed to production due to high gas production. Following the shutoff interventions, those wells were put back in production with an average reduction of 8.0 MMscf/d in gas produced per well and an average increase of 600 BOPD in oil produced per well. Near the end of the campaign, average oil produced per well reached 830 BOPD thanks to further improvements in the operational workflow. This approach constitutes a significant step forward in terms of efficiency and economic sustainability. The use of CT to perform all the stages of conformance operations greatly improved logistics on the platforms. In addition, the real-time monitoring capabilities of the system and flexibility of its downhole toolstring enabled an enhanced level of evaluation throughout the interventions, which, in turn, optimized the outcome and saved days of operation.