Well Stimulation in the North Sea: A Survey
Authors: LaFleur K.K. , Johnson A.K. 
Published: December 2007

This paper was prepared for the Second Annual European Meeting of the Society of Petroleum Engineers of AIME, to be held in London, England, April 2–3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
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ABSTRACT:
Well stimulation practices in the North Sea have been surveyed. Matrix acidizing and fracturing with a seawater based fluid are discussed and results presented.

INTRODUCTION:
In the past six years widespread use of well stimulation techniques has been made in the gas wells of the southern North Sea Basin. Generally speaking, wells in the Indefatigable and Leman Fields (Rotliegendes formation) require a treatment for formation damage removal only, West Sole Field (Rotliegendes formation) wells require fracture stimulation, and Hewett (Bunter and Hewett Sandstone) and Viking Field (Rotliegendes formation) wells achieve optimum production without stimulation or a treatment for damage removal.
Since the majority of these treatments have been performed in the Rotliegendes (Basal Permian) sandstone formation, a survey has Permian) sandstone formation, a survey has been made of all available data in an attempt to determine which particular treatment designs have been most successfully applied.
Net pay in the Rotliegendes formation is typically 100 to 300 feet with an average porosity of 15 to 20 percent. Permeabilities vary widely.
Pressure build-up and draw-down tests of the Pressure build-up and draw-down tests of the gas wells completed in the Rotliegendes formation show high formation damage in wells of higher permeability following initial completion. Those wells of low permeability generally do not show very high damage, although production is often below what is considered economically acceptable. Generally, the wells having higher permeability have responded to acid stimulation permeability have responded to acid stimulation while those of lower permeability have required fracture treatment.

ACIDIZATION:
Most of the data available on acidization has been drawn from the Rotliegendes formation in the Indefatigable and Leman fields. Whether intentionally or not, all wells investigated were matrix acidized rather than fracture acidized.
Matrix acidization uses the technique of treating a formation at pressures below that required to initiate a fracture, i.e. at pressures below the bottom hole fracture pressures below the bottom hole fracture pressure (BHFP). pressure (BHFP). Fracture acidizing is the technique whereby acid is used to hydraulically induce a fracture, then give that fracture conductivity by the dissolving reaction of the acid with the fracture face.