Propped-Fracture Stimulation From a Jackup Rig in the North Sea
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 126320, ’Propped- Fracture Stimulation Performed From a Jackup Rig in the North Sea,’ by Bruce Robertson, SPE, and Elizabeth Ridley, Halliburton, and Bryan Atchison, Silverstone Energy Limited, prepared for the 2010 SPE North Africa Technical Conference & Exhibition, Cairo, 14-17 February. The paper has not been peer reviewed.

Proppant-based hydraulic-fracture stimulation in the southern North Sea is becoming increasingly popular and, in some marginal fields, can be crucial to maximize reservoir contact, thus improving deliverability from tight-sandstone gas formations. Because of the low availability of purpose-built or temporary stimulation-class vessels in the North Sea, an alternative concept was pro-posed to place more than 250,000 lbm of proppant into Well 49/17-14 from the Ensco-100 jackup rig. 

Introduction

Well 49/17-14 is in the Victoria field in the UK sector of the southern North Sea. The block, approximately 135 km east of the Lincolnshire coast, contains the Viking, Victor, and Vixen Rotliegendes gas fields. Exploration Well 49/17-14 was drilled vertically in a crestal position in 2006 and 2007. Some 150 ft of core was recovered, and, after drilling, 27 formation-pressure samples were obtained. Two cement plugs were set to isolate water-bearing sands, and a 7-in. liner was run and cemented.

Generally, wells in the Indefatigable and Leman fields (Rotliegendes formation) require treatment only for formation-damage removal. Studies of the Victoria field, as with several of the tight-gas-sand formations in the southern North Sea, indicated that an effectively designed and executed hydraulic-fracture treatment would accelerate and increase overall recovery by more than 85% over the expected life of the well. It became clear that a fracture treatment was required to deliver the well successfully. Therefore, planning operations began with the objective of performing a hydraulic fracture on the zone of interest to improve the relative conductivity of the residual hydrocarbons in the formation, depositing sufficient volumes of proppant to help prevent fracture healing while avoiding propagation of the fracture into the water-bearing interval approximately 315 ft below the reservoir-formation top.

Preparation and Planning Because of the complex and logistically challenging nature of the operation—which involved having well-test, wireline, fracturing, filtration, coiled-tubing (CT), and nitrogen equipment on the jackup simultaneously—project planning and preparation were prioritized with regular planning meetings to develop an initial-action log and to ensure completion of assigned activities. During this process, an appreciation of the scale of the entire operation was gained by all service companies and vendors involved. In addition to the managed action tracker, several reviews and risk assessments were conducted, with input from all vendors identifying and suggesting methods to improve operational efficiency and help minimize risks and hazards. The output from these meetings helped rig crew and vendors become familiar with each other and with the operation being planned. Because input was gained from the entire operation, a desire to succeed became a byproduct because all were part of the planning process.