Harsh Environment HP/HT Gas-Condensate Production Cleanup Experiences—Kristin Field

Abstract

This paper presents the well clean-up experiences for the Kristin HPHT gas-condensate field. The paper covers the production clean-up campaign design, including up front planning, job design, technology selection and review of the test results vs. the objectives. The paper also addresses requirement for safety and environmental considerations. Traditional production clean-up methods and equipment has evolved over the years, adapting to changing authority and operator requirements, whilst striving to be more cost effective when it comes to operational cost, particularly in NPT terms. This has resulted in more complex equipment packages and much stricter environmental and safety requirements. This paper will demonstrate how the above was addressed for the Kristin field development project and how the results compared with the set goals. Descriptions of the key design criteria and technology selection for HPHT gas--condensate well clean-up is covered together with the evolvement of these over time through the well clean-up campaign. Introduction Kristen is an HPHT gas condensate field, situated in the Haltenbanken area outside Mid Norway (Figure 1). Kristin was discovered in 1996 and has been developed with four sub sea templates with a total of twelve wells (Table 3), producing to a semi submersible production platform (Figure 2). Completion of the first well was finalized on May 1, 2005, production commenced on 3 November the same year. Reservoir properties vary greatly over the field, and between the different reservoir zones. Highest permeabilities are found in the Ile and Tofte Formation with permeabilities in the Darcy range, while the Garn formation has permeabilities ranging from 1 to 10mD. Although Ile has better properties than Garn, Garn contains the major part of the field reserves. The virgin reservoir pressure is 910 bar at a depth of 4800 m TVD MSL. The fluid system is a retrograde gas-condensate system, with a GOR of approximately 1000 Sm[3]/Sm[3] and dewpoint pressure of 400 bar at reservoir temperature. In most of the wells, 7" liners have been run across the reservoir and then orientated perforation conducted. Most of the wells are drilled at high angles through the reservoir with 85º with a corresponding pay zone of 830 m being the record. The wells are perforated in oil-based mud. After perforating, a barrier valve is run above the liner hanger and the rest of the well is then displaced to clean completion fluids. Some of the wells are penetrating sands that are too weak for orientaded perforations to be used as a sand control measure. In these wells 5½" screens are run in oil-based muds before the barrier valve is run above the screen hanger. When the well is ready for start-up, about 50 m[3] of packer fluid (30/70 MEG/water) is located inside the tubing. 10–30 m[3] of oil-based mud, in many cases with considerable amounts of perforation debris is located below the barrier valve. The maximum shut-in pressure at the subsea well head after a flowing period has been recorded to 722 bar. For many wells flowing well head pressures have climbed well above 600 bar. (Table 1 contains additional field information.) To ease start-up of the wells towards the production facility, the operator demanded that the wells first be cleaned up towards the testing facility onboard Scarabeo 5 via a Workover Riser with Flowhead (3rd party supply). The overall goals for these cleanups were:Retrieve packer fluid and drilling mud from the well.Perform a short production test including a build-up to determine well and reservoir characteristics.Accomplish the technical goals without damage on humans, well/equipment or disposals to the environment.

Optimization of Chock Valves for Fracture Clean-up in Tight Gas Condensate Reservoirs

“…The efficiency of clean-up in tight gas condensate reservoirs has a tremendous effect on the productivity of gas-condensate wells. 4,5,6 Fracture-fluid clean-up efficiency is highly related to proppant volumes, multiphase flow, proppant crushing, polymer filter cakes and yield stress of concentrated gel in fractures. 7,8 Recommendations to improve fracture clean-up efficiency have been made in previous work, 9 including chemical additives, 10,11,12 water evaporation, 13 coated fracturing proppants, 14,15 and microwave heating.…”