One of the most common challenges in deepwater environments is hydrate formation during drilling or well testing operations. A hydrate is generated in the presence of a combination of the following four elements: water, natural gas, low temperatures and elevated pressures. The hydrate has the appearance of ice structures and can form very quickly. Hydrates are normally generated during operations such as startup, shutdown, blowdown, and bleeding. In the deepwater oilfields of Brazil, operators have been faced several challenges during hydrate remediation interventions, including:Effectively removing the hydrate plug formed in the riser without damaging the tubing, downhole valves, and subsea tools across the blowout preventerReducing risk of hydrate formation due to unpredictable behavior because the hydrates can be very hard and very strong, holding high-differential pressures, potentially making a projectile of the formerly plugged objectLimiting pressure losses through the umbilical and maintaining injection rates of methanol and monoethylene glycol (MEG)Resuming well testing operations with the least amount of lost rig time. From a drillship, we applied a combination of chemicals pumped through a high-pressure rotating nozzle deployed with coiled tubing (CT). The hydrate plug was breached in less than 4 hr. This cleaning operation effectively removed the hydrate plug and cleaned the tubing, enabling the Operator to resume pressure/volume/temperature testing operations of the deepwater well.
During the last 30 years, in offshore Mexico, matrix stimulation treatments were designed and executed around pumping large volumes of fluids by a "bullheading technique," which comprised multiple stages of pre-flushes, acids, and solvents without adequate control of placement. The objective of these matrix stimulation treatments in the Ku-Maloob-Zaap carbonate formations fields is to remove drilling-induced damage and achieve maximum well productivity. This is a challenge because this formation is naturally fractured and presents high permeability, around 4-5 Darcies. The "bullheading technique" has been proven to be inefficient because the evaluation logs have shown non-uniform stimulated intervals.Recently, coiled tubing (CT) operations adapted a new procedure to improve the stimulation treatment's placement technique. However, the biggest concern was to determine if the chemical fluids had correctly stimulated the target zones. The initial solution was achieved by pumping radioactive tracers with the chemicals during the stimulation and an additional CT run performed to take a gamma ray (GR) log. This procedure has proven to be inefficient and time consuming.For first time in offshore Mexico, the innovative technique of combining coiled tubing equipped with optical fibers (CT-EOF) and distributed temperature survey (DTS) to acquire and record pressure and temperature data-which is compared with petro physical data in real time-to decide selective placement of chemical fluids in target zones, was implemented in a completed oil producer cased hole well in Campeche Bay. This innovative technique reduced operational time and eliminated the additional CT run while optimizing the placement of the stimulation fluids for improved well productivity. The information obtained from the DTS allowed informed decisions to be made on alternative lifting methods to improve the well productivity performance for this well.The job design, execution, and post-treatment evaluation of a matrix stimulation treatment in well M-432-where CT-EFO and DTS were combined-will show how the operation was optimized. In addition, the comprehensive analysis from DTS data was used to optimize placement of the stimulation treatment, the evaluation of effectiveness of the matrix stimulation treatment, the analysis used to identify the well productivity problem, and the benefits this new technique offers in the Ku-Maloob-Zaap carbonate formation.
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.
Over the last years the oil and gas Mexican operator's exploration and development programs are becoming more challenging due to the complex conditions where hydrocarbons are found today. One of the areas that have seen a decline on production over the years is the offshore. As an alternative to find new sources of oil that overcome the current production decline in the area, the operator is drilling new wells where the operational capabilities of the equipment are put out of their limits. These new wells are drilled at depths beyond the conventional 5,000-m (16,400-ft) with bottom hole pressures as high as 15,000-psi and temperature over 180ºC requiring that the equipment providing the services over their producing life reach their own limitations and in some cases re-engineering of the design and process has to be done.In some cases, minimum changes to the equipment or processes are enough; however, a service of such complexity as the use of Coiled Tubing (CT) requires a major review of all the components of the operation to be completed in order to reach the new targets without jeopardizing the safety of the operations and/or compromising the production of the well. This paper details the CT string design criteria to reach the deeper vertical depths with high wellbore mechanical friction coefficients while withstanding high pressures; equipment selection, to allow greater CT length capacity on reel and higher pulling capacity on injector head; platform and crane specifications to withstand over dimensioned equipment, as well as, a case study to analyze equipment and CT string performance for interventions on these types of wells.
Coiled tubing (CT) operated from a floating anchored vessel (FAV) was developed for well intervention in offshore locations where crane limitations and deck loading constrains imposes various limitations on the ability to perform workover operations. This tailor-made solution involves the operation of a CT unit with the tubing reel located on a FAV and the injector head positioned on the offshore platform. Today, CT operations supported by a FAV are routinely performed in several countries, including Malaysia, Gabon, Tunisia, Brunei, Angola and the North Sea. The first CT operation supported with a vessel in the Gulf of Mexico was successfully performed in a non-producing well which had been shut-in for nine months due to compatibility issues with the structure for temporary installing service equipment and and the limited availability of jack-up platforms to provide a deck area for positioning CT equipment. As result of this successful operation, a new perspective of CT rigless interventions was adopted in offshore Mexico, thus allowing the operator to improve equipment utilization for both CT units and workover rigs, in order to maximize oil production. This paper details the analysis, execution and evaluation of the first CT operation from a FAV in offshore Mexico, which includes equipment selection, sea condition and weather-related studies, contingency planning, personnel competency and training requirements, and logistical considerations, among other technical factors that were critical in the implementation of such project. As well, the benefits that were realized by the operator regarding production enhancement and operational cost reduction are covered.
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