Abstract

Hydraulic fracturing using proppants is a well established technique for increasing well productivity. However, uncontrolled mineral scale deposition within the proppant pack can result in reduced conductivity and fracture performance, thereby devaluing the initial investment in the fracture. To protect this investment an active scale control strategy is required especially when executed in the presence of a water flood. A number of different techniques have been proposed and used historically, however they have all suffered with one or more drawbacks. These drawbacks have included excessive volumes, poor placement control, short treatment life and / or the potential for fines and sand generation and pack instability. The ability to place scale inhibitor within the voids of a porous proppant offers a robust technique for placing a large amount of scale inhibitor throughout the proppant pack while its controlled released protects the productivity of the fracture.

Previous papers have described the development of porous, scale inhibitor impregnated proppants and highlighted the initial returns from field trials performed on land wells on the North Slope of Alaska. The impregnated proppant technology has now been further developed and two treatments have recently been deployed in the North Sea. The treatments were both designed to stimulate production and to protect the fracture against future scaling scenarios.

This paper will describe the design criteria used to select this method of protecting the future performance of the fracture. In addition this paper will describe the design and execution of the treatments while highlighting the fracture performance and scale inhibitor return profiles generated by recent treatments performed in the British and Norwegian sectors of the North Sea.

Introduction

The deposition of inorganic scale during the production of hydrocarbons is a major problem. The primary effect is deferment of oil production due to scale deposition in the near well bore and tubing of production wells as well as in the proppant packs of hydraulic fractures. Scaling problems are currently managed by the use of preventative and remedial chemical treatments that often involve significant costs to the operator, especially in advanced and deepwater wells1–4.

Previous papers have described the development of porous, scale inhibitor impregnated proppants (SIIP) and highlighted the initial returns from field trials performed on land wells on the North Slope of Alaska5–7. However, the North Slope of Alaska is considered to be a very low humidity environment, and the SIIP had not been deployed in high humidity environments where long-term storage may become an issue. The SIIP technology has therefore been further developed to produce a stable product suitable for deployment in the high humidity environments encountered offshore onboard a stimulation vessel. Two treatments have recently been deployed in the British and Norwegian sectors of the North Sea. The treatments were both designed to stimulate production and to protect the fracture against future scaling scenarios.

Background
Hydraulic Fracturing

This production enhancement technique involves injecting into the formation at pressures above the parting stress of the rock. The pressure required is dominated by the formation depth and mechanical properties combined with residual tectonic stresses and not physical tensile strength of the rock.

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