Case Study: Oilfield Completion Technology and Reservoir Analysis Optimizes Injectivity for Geothermal Water Production in the Netherlands

Abstract The Greenport Westland-Oostkand is a geothermal heating project near Maasdijk, Netherlands; it comprises 153 doublets within a 170km2 area with the potential to provide 25% of the heat for 30 years. Within are two target sandstones with several wells drilled. Unfortunately, some wells experienced sand production and integrity challenges. Our client's objective was to optimize the connection of wellbore-to-reservoir, a critical factor for the success of water injection and water production in geothermal doublets. The reservoir requires specific key attributes (i.e., adequate temperature, porosity, permeability, structure) to be a good source rock; however, these factors are in-situ and not changeable. Variables available to manipulate for optimum flow are the completion design (i.e., type/ size of casing, type/rate of injected/ produced fluid, perforating scheme). Examples are the specialized casing design using glass-reinforced epoxy (GRE) liner to protect from highly corrosive salt water. Also, using oilfield completion techniques consisting of a Tubing-Conveyed Perforating (TCP) system, conveyed on Coiled Tubing(CT), and Dynamic Underbalance (DUB) to provide optimal perforation tunnel cleaning. Study discusses the innovative technologies used to ensure a 30-year life. This includes the process and innovation behind the devices (e.g., inter-gun centralizing roller subs) used to protect the GRE-lined casing. If damaged, this can cause leaks and failure, leading to costly intervention, well abandonment, and especially heat loss for surface facilities. It also discussed advanced perforating design driven by rock mechanics based on pre-job modeling to optimize the perforating gun to optimize clean tunnel formation. However, limitations applied, forcing the use of several different charges: 1) For injection wells, perforating geometry required smaller hole/longer penetration, provided by Deep-Penetrating (DP) charges. 2) For producing wells, perforating geometry required large hole/shorter penetration, provided by Good Hole (GH) charges • For both of these, perforation flow was optimized by dynamic underbalance surge-cleaning. 3) For second runs on both well types, since wellbore now has open perforations and is at balanced condition, required innovative "reactive" DP charges- these provide exothermic reaction within perforation tunnel for cleaning, since dynamic underbalance was no longer valid. Success was evaluated by post-job well flow analysis using Production Logging Tools (PLT), Injectivity tests, and production flow tests. Advanced modeling techniques supported this. This novel application required the development of bespoke equipment and innovative use of existing technologies: 1) Centralizing roller subs were designed/manufactured to protect the GRE-lined casing. 2) New application of perforating geothermal wells required specialized charges and dynamic underbalance technique. 3) For safety reasons, the long perforating gun interval conveyed on coiled tubing required breaking the system into two runs. Since dynamic underbalance was no longer valid, "reactive" shaped charges were used for tunnel cleaning.