Test Methodology Optimizes Selection of Fluids for Gasfield Development
Authors: Carpenter Chris 
Published: February 2020

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 195601, “Systematic Selection of Drill-In and Completion Fluids for Development of the Dvalin High-Temperature Gas Field,” by Oliver Czuprat, SPE, Bjorn Olav Dahle, and Ulf Dehmel, DEA, et al., prepared for the 2019 SPE Norway One Day Seminar, Bergen, Norway, 14 May. The paper has not been peer reviewed.
For the development of the Dvalin high-pressure/high-temperature (HP/HT) gas field in the Norwegian Sea, a completion scheme using standalone screens is planned. To secure maximum cleanup and productivity, even after long-term suspension, comprehensive laboratory testing was performed to evaluate specific properties from drilling and completion fluids at downhole conditions. The complete paper details the results of all test phases. With the test methodology, several proposed mud-system candidates were disqualified at an early stage, thus saving time and cost for subsequent formation-damage testing and complementary analytics.
Introduction
Formation damage is believed to have caused difficulties in modular-dynamic-tester sampling in the high-permeability zone of Dvalin West. The damage mechanism has been investigated in a study that revealed both fluid systems to have good fluid-loss-control properties, as observed in drilling operations. However, both systems showed damage potential. The extent of damage is more pronounced in Dvalin West.
The field-development plan calls for four producing wells to be drilled (two in each structure). Prevention or, realistically speaking, minimization of impaired production as a result of formation damage has been identified as a priority. A completion scheme with standalone screens requires additional specific properties from drilling and completion fluids at downhole conditions. The production facilities will be commissioned after the completion of drilling, and there are no provisions for handling cleanup flow through pipeline and topsides. Thus, all wells will be cleaned up to a temporary test plant on-board the drilling rig. The lag time between drilling the wells and cleaning them will be 2–3 weeks, underlining the necessity of a drilling mud that is stable over a significant period of time while retaining inherent mobility.
Six reservoir drill-in fluids (water- and oil-based) were proposed by different vendors, and samples thereof and the corresponding screen fluids (if available) were provided. The systematic test program consisted of a sequence of four test phases, where only successful fluids went to the next phase (Fig. 1). A description and application of equipment and processes is provided in the complete paper.
Data and Results
Phase I. The first test phase comprised a set of simple screening laboratory tests. The best-in-class drilling and completion fluids from the study were then tested with regard to formation damage (return permeability tests). Tested qualities included density, particle size distribution, rheology, mobility, settling, emulsion stability, HP/HT filtration and rheology, compatibility, and production-screen testing. As detailed in the complete paper, many of the fluids demonstrated acceptable or good performance in many of these aspects; nevertheless, on the basis of observations during Phase I, two out of six fluid systems could already be excluded as unstable for the application (Drilling Fluids 1 and 6).