SPE 26042

Prudhoe Bay Rig Workovers: Best Practices for Minimizing Productivity Impairment and Formation Damage

C. G. Dyke, BP Exploration Operating Co. Ltd., and D. A. Crockett, ARCO Alaska Inc.

SPE Members

Copyright Society of Petroleum Engineers, Inc.

This paper was prepared for presentation at the Western Regional Meeting held in Anchorage, Alaska U.S.A.

This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should not contain conspicuous acknowledgement of where and by whom the paper is presented, Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A. Telex, 163245 SPEUT

Offshore Magazine

August 1991 edition

Driller tests solution to stuck pipe problems

Preventative drilling fluid treatment alternative to diesel fuel pills

Jack C. Estes; consultant, Buford Gill; Grace Drilling Company

Stuck pipe is more than just a nuisance - it is a costly problem for operators and contractors. It is especially frustrating to the people on the rig who are keeping drilling fluids within specification, and keeping the drilling pipe moving. There are about as many reasons for pipe getting stuck as there are drillers who have been stuck. Years ago, there were fewer reasons, and all of them boiled down to just one reason - "bad mud." It was easy to blame the mud, when it weighed several points more than required, and solids control equipment was just about non-existent or barely working.

High Temperature Testing Procedure

Liquid Casing® has recently been evaluated in the laboratory under simulated field conditions by STIM-LAB Inc. in Duncan, Oklahoma. This study used a kill-fluid formulation where Liquid Casing® was incorporated into a polymer based formulation.

The test work was carried out with equipment designed to evaluate formation damage under dynamic flow conditions of fluid. The test fluid was in contact with a sandstone core with an effective permeability of about 250 md as determined at 250 °F with laboratory prepared North Sea sea-water. The core was mounted in a Hassler sleeve under a closing pressure of 1,500 psi. The test fluid could be flowed past the face of the core with a differential pressure of 1,100 psi across the length of the core. The filtrate was collected in a pressurized container with 100 psi back pressure so the actual pressure drop across the core was 1,000 psi. Both the fluid and the core could be heated to the required temperature. The filtrate volume could also be determined as a function of time.

Return Permeability Study

The non-damaging nature of Liquid Casing® to producing formations was evaluated in an extensive laboratory test program carried out by STIM-LAB Inc. in Duncan, Oklahoma (File Number SL 1815.).

Formation evaluation studies used two types of formations with a 2% (7 lb/bbl potassium chloride (KCI) brine containing 4 lbs/bbl Liquid Casing® and polymers of either Xanthan gum or Xanthan gum plus some polyanionic cellulose (PAC). The properties of the fluids tested are given in the following table.

Biological Degradation Study

A twenty eight day marine BOD was determined by a procedure following the OECD Guideline for Testing of Chemicals 301D - Ready Biodegradability: Closed Bottle Test modified to marine conditions and carried out by Cross and Bevan Water Services, Bedford, England. Thus, the biological "seed" was obtained from the River Crouch Estuary, as recommended by the Ministry of Agriculture, Fisheries and Food, and artificial sea-water prepared from Marinemix was used as the diluent. The salinity of the dilution water was 33.6 g/l NaCl and the pH was 8.0.

Toxicity Studies

The toxicity of Liquid Casing® was evaluated in a Report by Weintritt Testing Laboratories in Project Number 319-12-5808.

Liquid Casing® was suspended in sea water and the survival of Mysid shrimp (Mysidopsis bahia) was determined over a 96-hr. period. The test results are summarized in the following table.