The plug-and-perf (PnP) method is widely used globally for multistage fracturing operations. With only a few jobs performed worldwide, coiled tubing (CT) assisted PnP operations in high-pressure/high-temperature (HP/HT) wells are largely uncharted and most challenging. The "A" field in India has HP/HT formations, with bottomhole temperature (BHT) of 310°F and reservoir pressure of 9,000 psi. Whereas the PnP method is widely used globally, there are few examples in wells with completion restrictions or whose downhole conditions dramatically increase depth inaccuracies and equipment damage. This study describes how to address challenges such as depth correlation (which affects plug-setting depth accuracy), low injectivity, completion restrictions, and heavy brines (which damage CT). To gain further understanding of operations, simulations are sensitized to identify solutions for pumping rates, HP/HT conditions, well kill fluid, milling, and cleanouts where obstructions hindered BHA penetration. The proposed best practices presented here are for primary CT operations involved in the complete PnP cycle, such as wellbore displacement, well dummy run-drift, setting the isolation plug and milling, acidizing using jetting tools, sand cleanout using gels having best performance in HP/HT environment and motor-mill runs with durable resistance in harsh environment, well kill (using 13.65-ppg calcium bromide), and nitrogen lift. The featured case studies describe operations including seven bridge plugs being set at accurate depths and milled after fracturing; cleanout of a 340-m sand column is also featured, as well as well kills with heavy brines. Optimized operational parameters such as CT speed, pumping rates, and the use of smaller outer diameter bottomhole assemblies doubled operational efficiency during those operations.
Coiled tubing (CT) sand plug operations associated with multistage fracturing operations in high-pressure/high-temperature (HP/HT) wells are very challenging, in part because of the small number of such jobs that have been performed worldwide. The wells in "A" field in India have HP/HT formations, with a bottomhole temperature (BHT) of 310°F and a reservoir pressure of 9,000 psi. Although millable bridge plugs are preferred industry-wide, this case illustrates how sand plugs become a suitable alternate solution for multistage stimulation to address space limitations, equipment and completion restrictions, and small tubing sizes, even in challenging downhole conditions. This study provides solutions to operational challenges of low injectivity and completion restrictions, which preclude bullheading and use of conventional bridge plugs. Simulations were sensitized to identify the best solutions for sand settling time, HP/HT conditions, pumping rates, CT speeds, and cleanouts where calcite or scale deposits on sand hinder bottomhole assembly (BHA) penetration. Best practices are given for sand plug operations in challenging HP/HT environments; those best practices can be applied as a reference to design, prepare, and safely perform CT sand plug jobs in such conditions around the world. To address operational challenges in the cases presented here, the first three stages were bullheaded and the last two (a total 325-m sand plug) were placed using CT. Wireline was run to verify CT sand plug tag at ×200-m measured depth (MD). After the successful refracturing job, the 340-m sand plug was cleaned out, followed by acid spotting and squeeze using CT to rejuvenate the lowest zone. Strict application of the recommendations prevented the occurrence of operational contingencies, such as stuck CT, sand bridging, and settling of sand in surface equipment.
Executing interventions in wells encrusted with wax is challenging because experience with global coiled tubing (CT) dewaxing operations is limited, and equipment failure and stuck pipe risks are high. With few jobs performed worldwide, CT dewaxing (hot oil circulation with CT) operations are largely unexplored. The deviated wells in a field in northeast India pose several challenges including completely seized wellbore due to paraffin/asphaltene deposition, previous failed well cleanout attempts, very slow and low bottomhole assembly (BHA) penetration, pumping corrosive and flammable low wax crude (LWC) through CT, high chances of CT getting stuck, and pumping heated 69°C LWC through the CT. This case study delivers insights about design, safety, and operational considerations for 1.5-in. CT dewaxing and nitrogen lift operations in a subhydrostatic well in the field. The objective of this CT dewaxing and nitrogen kickoff operation was to clear the well of paraffin/asphaltene/wax to 1600 m and activate it with nitrogen, and this paper describes solutions for cleaning out and nitrogen-lifting wells with declining production due to paraffin and asphaltene deposition. One well is described in this case study, but this approach can be used perform CT intervention in similar wells. For this case, simulations were sensitized to identify the best combination of pumping rates, CT speeds, and fluid temperature to remove deposits hindering BHA penetration. This study proposes prevention measures using appropriate grounding and procedures, which determine if the crude oil can be pumped through CT. By use of this methodology, 581 dewaxing runs have been performed in 78 wells. Extensive on-job experience and lessons learnt by performing this operation over the last 3 years bring excellent results and prevent misruns. In many cases, production has been restored from nil; several examples feature a fivefold improvement of productivity thanks to this intervention method. Optimized operational parameters such as CT speed, pumping rates, and the use of smaller outer diameter BHAs doubled operational efficiency during those operations. In addition, strict application of the recommendations prevented the occurrence of operational problems such as stuck CT, crude oil flashing, sand bridging, and equipment failure.
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