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.
The production curve of the main Mexican offshore fields has been decreasing rapidly year-on-year, representing a challenge to the eighth-largest oil producer country and an opportunity to implement new techniques for workover (WO) operations to increase production recovery.Within the most common WO activities developed in offshore Mexico is acid stimulation of carbonates, which was developed as pumping a large volume of fluids (solvents, HCl 15%, etc.) with minimum control for zonal coverage. Conventional coiled tubing (CT) jobs have improved this technique with the use of impact jetting tools to remove damage at the tubular and perforation holes and placing the treatment in the desired area. The estimation of fluid injection per zone has been evaluated using radioactive traces. However, the estimates of where the fluids go lack accuracy, and the radioactivity poses additional risks related to hazardous material handling.In 2009, a new interpretation technique to evaluate the treatment zonal coverage appeared that used CT with fiber optics. This distributed temperature sensing (DTS) enables the equipment to record temperature readings at several predetermined depths over time creating a survey that identifies, qualitatively, the admittance of the treated pay zones based on the formation's cold-down/heat-up effects. Unfortunately, this technique had some limitations as the data recorded needed to be converted, interpreted, and then translated into common oilfield language in the form of graphics and data tables. The time to get a final result from the readings to the customer was so long that the window to modify the current treatment to improve the well response was, on most occasions, already closed. DTS inversion brings a "real-time DTS matrix stimulation evaluation product" by using an inversion algorithm coupled with a fluid placement model to accurately quantify the amount of treatment placed across the treated zones of the well. A detailed case history from an offshore Mexico well describes the first worldwide real-time DTS inversion job and illustrates the workflow and advantages of this technique. The results from the technique showed a direct match with a previous evaluation of the formation through production logging conveyed on Wireline tools.
In offshore Mexico, operators have increased workover activity to maintain oil and gas production. The reservoir is a naturally fractured carbonate with gas and water flowing through the natural fractures, leaving oil trapped in the matrix. Controlling gas and water production is critical to prevent unwanted fluid from reaching the wellbore. Currently the combined progression of gas and water contacts has reduced the oil window from several hundred to as little as 40 m in some wells. In these conditions, and with rapidly advancing gas and water contacts, it is paramount to provide solutions to restrain unwanted fluid from reaching the wellbore. One of the most common workover interventions consists of isolating the water producing zone with coiled tubing deployed through-tubing inflatable-packers (CTD-TTIP) and perforating an upper oil-bearing zone. The problem is compounded by low reservoir pressure, resulting in heavy losses while drilling and cementing production zones; loss of zonal isolation as result of cement sheet failure through the producing intervals; and wells completed with a combination of large tubular sizes. Recently, operators and service companies in offshore Mexico have implemented an innovative workflow intended to enhance the effectiveness of water control interventions in this challenging work environment, through the utilization of realtime downhole measurements (RTDM) via coiled tubing equipped with optical fibers (CT-EOF) for accurate control of CT depth, the packer inflation process, packer differential pressure limits during the treatment injection, and fluid placement. This paper provides a technical analysis of the engineering process required to develop successful workover zonal isolation jobs with CTD-TTIP and RTDM in offshore Mexico, and presents a case history, lessons learned, conclusions, and recommendations from the experiences gained while performing CTD-TTIP with RTDM in offshore Mexico.
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