Drilling Fluid Programmes Can Reduce Hole Erosion And Minimise Hole Problems: Case Histories Offshore Vietnam

Abstract

AJ Twynam, PM Collins, MD Jackson, P Forman Abstract This paper describes technical studies undertaken at BP Exploration Technology Provision Centre and the application of these studies along with transfer of best practice and local knowledge to solve two specific problems encountered in drilling offshore Vietnam.Hole instability in shallow clastics: hole problems related to drilling shallow claystone sections with water based muds were being encountered; tight hole, bit balling, stabiliser balling, overgauge hole. This was causing lost time and increased costs. A technical audit involving the BPX Technology Provision Centre, Dowell IDF and BP Vietnam along with technology transfer from the North Sea Operations allowed the drilling fluid used on the problem section to be modified/optimised resulting in much improved drilling efficiency.Hole erosion in deeper clastics : the hole erosion encountered in deeper clastic sections of wells can lead to several problems, namely the failed attempts to secure adequate wellbore evaluation information in the reservoir section. Cores were available from problem formations and these were used in geomechanical and chemical analysis to ascertain the cause of the problem. Based on the findings it was possible to make recommendations to the drilling fluid programmes and drilling practices, which have lead to enhanced drilling efficiency and much improved wellbores. Introduction BP Exploration commenced drilling offshore Vietnam in December 1992 operating in Block 5.2, 6 and 118. Several technical challenges were experienced in the drilling of these wells, In an attempt to optimise on drilling performance, several studies were undertaken. This paper details two such studies undertaken by the BP Technology Provision Centre in Sunbury, UK. The first study was to carry out a technical audit on drilling fluids being used in an attempt to improve drilling performance in shallow clastic formations. The second study concerned the observed problem of washed out holes in the deeper clastic formations which had resulted in problems with adequate formation evaluation, This paper describes the problems as identified, the methods used to determine the cause of the problems and discusses the conclusions and recommendations resulting in improved performance. HOLE INSTABILITY IN SHALLOW CLASTICS One of the more problematic hole sections on wells in Vietnam (excluding the loss control problems in the carbonates) is the 17" /17-1/2" section through the shallower clastics. These sections were originally drilled using a gel/CMC system which was gradually upgraded to a KCL/Polymer (PHPA) system. Problems encountered on this section were due to water base mud" being used to drill shallow clay stones. (Bit balling, tight trips, reaming, shaker blinding, stabilisers caked up). This was leading to expensive mud bills, compromised drilling performance and poor quality hole.