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Abstract

The technical difficulty of constructing deep gas wells makes them costly items on any operator’s budget sheet. For this reason there is a powerful economic driver for the operator to use the best available well construction technologies that will deliver a deep gas well at lowest overall cost while ensuring that the well’s connectivity to recoverable hydrocarbons is not impeded in any way. In 1995 Mobil was the first oil company to use formate brines as drill-in and completion fluids to improve the economics of deep gas field developments.  Since then the formate brines have been used in more than 30 deep gas projects (amounting to at least 140 wells) by major oil companies such as Total, Statoil, BP and Saudi Aramco. These developments have included the deepest reservoir in the North Sea and the largest HPHT gas field in the world. This paper collates and categorises all of the statements relating to the performance of high-density formate brines in deep gas well constructions, as recorded in a number of white papers written by three long-term users of the brines. A review of these statements provides an insight into where and how the formate brines are delivering economic benefits in deep gas field developments. This analysis is complemented by a look at the production performance of two deep HPHT gas fields drilled and completed with formate brines in 2001/02. The cumulative hydrocarbon production from these fields is now already close to or exceeding 90% of estimated recoverable reserves.  The weight of evidence, supported by the sustained demand for formate brines in these applications over a period of 14 years, suggests that the use of formates introduces economies and efficiencies into deep gas field developments that are a) worth more in value than the overall cost of owning or leasing the brine and b) more rewarding than those provided by alternative well construction fluids.  

Introduction

It is estimated by the US Department of Energy (DOE) that the cost of constructing a deep onshore gas well in the USA is about 12 times that of the average conventional gas well drilled to 6,000 ft [Lambert et al, 2005].  The same source estimates that constructing the last 10% of a deep gas well in USA accounts for 50% of the overall well cost. This is a reflection on the technical difficulty of deep gas well constructions, and clearly indicates that operators need to pay particular attention to finding new ways of reducing costs while drilling and completing at depth.