The Greater Ekofisk Area: Addressing Drilling Fluid Challenges With Environmental Justifications

Abstract

This paper discusses the drilling related complexities of the Greater Ekofisk basin which have demanded innovative shale stabilizing mud systems. The innovative mud systems discussed include "pseudo and synthetic" oil emulsion fluids; and cationic water based fluids. Phillips Petroleum Company Norway (PPCoN) has improved drilling fluids standards and drilling/wellbore performance with environment awareness. The environmental evaluations of the innovative drilling fluids have involved a series of studies including Acute toxicity; Bio-degradability; and Bio-accumulation. In addition, marine seabed surveys have included studies to trace drilling fluids in the sea bottom sediments. The studies have revealed weaknesses in some test procedures. Through cooperation with external research laboratories, alternative test methods have been developed and evaluated. FIELD OBJECTIVES WITH DRILLING FLUIDS: The purposes for using the innovative drilling fluids have been clearly defined from the outset. This allows lateral strategy shifts while continuing through the testing and evaluation phase. This provides give/take opportunities for environmental considerations as they are better understood. The objectives are:The fluids selected must be of a standard which will allow problem-free drilling operations.The drilling fluids are to be reusable from well to well to minimize or eliminate discharges.The fluids selected must be environmentally acceptable when discharged coated onto cuttings. PRESENT FIELD CONDITIONS. THE EKOFISK FACILITIES The Greater Ekofisk region encompasses seven producing oil and gas fields. The drilling and production platforms primarily lie within an area of 35 kilometers north-south, and 21 kilometers east-west. The drilling operations involve 2/4A, B, C, D, E, K, 2/7A, and B platforms as well as the Embia field to the south-west of the region, and peripheral area exploratory wells. (See figure 1). The age of the platforms range from 6 to 18 years. Upgrading of the platforms is continuously being carried out to meet present and future needs. This includes the drilling fluids processing and storage areas. However opportunities to structurally modify these areas are limited. The structural limitations have helped stimulate the challenge of combining effective drilling fluids with the PPCoN commitments of improving environmental standards. FORMATION DESCRIPTION For each platform well, 20" casing strings are drilled and driven to approximately 1500 vertical feet deep. The 17 1/2" sections are drilled through soft clays to vertical depths of about 5000 feet. This section includes the Pleistocene; Pliocene; and top of the Miocene formation. The 12 1/4" interval is drilled through the higher pressured section of the Tertiary clays. The vertical depths of this interval are from approximately 5000 feet to 9500 feet. P. 261^

Study on Shale Gas Drilling Fluids Technology

“…In order to avoid the environment problem of diesel oil based drilling fluids and mineral oil based drilling fluids, synthetic based drilling fluids has been developed that has most of oil-based drilling fluids performance [8] . Synthetic based drilling fluids have huge advantages such as shale stability, lubricity and stain resistance, but the disadvantage is the high cost.…”