The well (Figure 1) of the case study presented in this paper is an oil producer from carbonate reservoir located in Southern Europe. Reservoir is characterized by a complex fracture network that increases the difficulties of production optimization actions, as for example water shut off interventions. This well is completed with a 4-1/2" liner extending to a 4-1/2" slotted liner inside a 6" open hole (OH). During the production time, the Water Cut (WC) has increased steadily finally reaching 94%, preventing the well from producing naturally. Log acquisition and interpretation, with Production Logging Tool (PLT) and Spectral Noise Logging (SNL), have shown that the water was coming from a fractures network laying behind the liner, to enter the top of the slotted liner despite swellable packers A and B. The lack of accessibility to this fractures network was therefore posing a challenge for an effective placement of a sealant gel.
Water production has always afflicted mature fields due to the uneconomical nature of high water cut (WC) wells and the high cost of water management. Rigless coiled tubing (CT) interventions with increasingly articulated operating procedures are the key to a successful water reduction. In the scenario presented in this paper, high technological through tubing water shut off (WSO) for a long horizontal open hole (OH) well in a naturally fractured carbonate reservoir leads the way to new opportunities of production optimization. Engineering phase included sealant fluid re-design: the peculiar well architecture and fracture systems led to the customization of a sealant gel by modifying its rheological properties through laboratory tests, to improve effectiveness of worksite operations. A new ad-hoc procedure was defined, with a new selective pumping and testing technique tailored to each drain fracture. The use of Real-Time Hybrid Coiled Tubing Services (CT with fiber optic system coupled with real time capabilities of an electric cable) made it possible to optimize intervention reliability. Details of the operating procedure are given, with the aim of ensuring a successful outcome of the overall treatment Sealing gels are effective in plugging the formation, but in fractured environments the risk of losing the product before it starts to build viscosity is high. The success of the water shut off job has been obtained by using specific gel with thixotropic properties for an effective placement. In addition, the pumping has been performed in steps, each followed by a pressure test to assess the effectiveness of the plugging. Results are compared to two past interventions with equal scope in the same well: a first one with high volume of gel and an unoptimized pumping technique through CT and a second where a water reactive product was pumped by bullheading. The selective and repetitive approach pumping multiple batches of sealant system with CT stationary in front of a single fracture provided the best results from all three techniques. The real-time bottom hole data reading capability provided by hybrid CT allowed the placement of thru tubing bridge plugs (BP) with high accuracy and confidence with the ability to set electrically, therefore reducing risks related to hydraulic setting tools (i.e. premature setting). This also allows continual pumping during the run in hole (RIH) to clean up the zone prior to setting the BP. The combination of this innovative pumping technique and customization of the sealant fluid made it possible to achieve unprecedented water reduction in the field. The high technology CT supported the operation by providing continuous power and telemetry to the bottom hole assembly (BHA) for real time (RT) downhole diagnostics. Moreover, the operating procedures offer basic guidelines to successfully perform water shut off jobs in any other reservoir independent of its geological nature and structure.
In a dual completed well, a through tubing perforation experience from geologic and reservoir study to job execution, is presented. Job targets have been the maximization of the production gain from one production string and the reduction of possible issues associated to charges detonation for the second string. The success of this job has been crucial for the life of a mature naturally fractured carbonate oil reservoir by opening new production opportunities. The experience has started with a reservoir study followed by a log acquisition to confirm the geological hypotheses about the lack of production contribution from a level. Once the level potential was confirmed, a review of all the possible technologies available in the market, with related benefits and disadvantages, has been carried out in order to obtain the maximum result in terms of perforation efficiency and minimize the risk to lose integrity or accessibility in the well due to charges detonation. A complete explanation of the overall work flow is provided to clarify all the decision making process. The first need to find an indication about the production contribution of a cased and cemented level through the hydraulic communication with a second perforated level open to production, can come from noise signals generated from a vertical flow path in formation. In fact, the vertical primary permeability or the natural system of fractures in a carbonate reservoir may represent a likely road to flow. The most suitable technology available to detect this phenomenon is the spectral noise log, which is a precise mean to discriminate about fluid movements in well or near wellbore according to its noise frequency. The second need to increase perforation efficiency and preserve one of the two strings from charges detonation in the second string, can be achieved by identifying a preferential direction at bottom hole and aligning the perforation guns to it. The analysis of real time data acquired through electric wireline from the "Magnetic Orientation Tool" coupled with a downhole electric motor controlled from surface, has allowed to fulfill this task. The study presented offers a valid workflow to follow for through tubing perforation jobs to restore uneconomic wells life and provides a base for spectral noise log possible uses and innovative tools to add in perforation bottom hole assemblies to have more reliable information for improved job results.
The paper describes the execution of a successful rigless intervention solution deployed to establish well integrity and restore well production in a field in Europe. The paper will go through the planning and execution of the job highlighting the criticalities encountered and the overall benefit of the activity. The approach used was a deep analysis of the well integrity issue from several prospectives. A new opportunity in the production optimization fluid has been identified. After an open discussion between Customer and contractor, a customized blend and detailed pumping procedure was agreed upon to reach the final scope. An injectivity test was executed to align the procedure to the reservoir and well behavior. Several pressure tests were performed to confirm the remedial job in place, and, after that, the well was re-perforated and opened to the production. The horizontal well described in the paper, shut in during 2016 due to formation damage and depletion was selected for a new through tubing perforations interval by coiled tubing in the horizontal section. An unexpected firing head activation occurred at an unplanned depth, just above production packer. This event produced communication across the production tubing, liner, casing, and formation, which immediately induced total losses into the naturally fractured carbonate reservoir causing well control issues. The accidental perforations could have jeopardized the final scope of the project with no oil production and premature well abandonment. A successful rigless remedial intervention was immediately executed to restore well integrity by using a real time fiber optic coiled tubing acquisition and a new conformance fluid combined with a customized cement packer technique. The remedial intervention allowed the operator to resume the initial project's scope of opening the new perforation intervals, restoring an important oil production of about 150 [m3/d]. The final solution utilized a product with unique thixotropic properties which was then engineered for production optimization using a detailed pumping strategy. This novel approach added significant value, as the operator was able to restore the integrity of the well in rigless mode, avoiding the associated rig cost.
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