Abstract

Sarawak Shell Berhad and Sabah Shell Petroleum Co Ltd are companies of theRoyal Dutch/Shell group of companies operating in Malaysia under a ProductionSharing Contract arrangement. Current drilling activities are located offshorethe states of Sarawak and Sabah. Due to difficult downhole drilling conditions, the use of synthetic based mud's have become increasingly more important.

In 2005–6, several deepwater locations will be drilled using non-aqueousbased drilling fluids. Of key interest is the availability of paraffin basestock from Shell MDS (Malaysia Sdn Bhd.'s plantin Bintulu). Paraffinbased systems are currently in use and found to be effective by other operatorsin the area. Because paraffins do not currently meet all US EPA laboratory testcriteria (toxicity and biodegradability), there is a strong interest incollecting actual field data to assess the environmental fate of suchdischarges. Shell Malaysiais embarking on a unique field study program toassess the fate of the paraffin based mud's and cuttings in water depthsranging from 300–1,500 m and to compare the data to similar studies withinternal olefin mud's.

Shell Global Solutions International B.V., with experience in SBM's anddeepwater environmental monitoring, had designed an approach to answer the keyquestions. The primary local contractor on the project is Petronas Research andScientific Services Sdn. Bhd. (PRSS). Metocean data from the study area isbeing used, in conjunction with a state of the art drill mud dispersion modelto predict the 3-D accumulation of the cuttings and mud on the seafloor. Gaschromatographic techniques (GC-FID) will be used for identifying andquantifying the presence of paraffins in the marine sediments. Ecological riskmethodologies are being used to predict potential benthic impacts. Each of fourdrilling locations will be sampled post drilling and one year later. This willprovide important insight into the weathering rates of paraffins insediments.

The study design, methods to be employed, and preliminary modeling andecorisk evaluations are presented and discussed in the paper.

Introduction

Background. For more than a decade, there has been a steady evolutiontowards the use of more environmentally friendly and better performingsynthetic based drilling fluids. Earlier experiences in the North Sea with oilbased muds (diesel), and later mineral oil based systems, indicated significantimpacts on nearfield benthic environments. In most of these cases, drillingdischarges where shunted near the seafloor, and involved significantaccumulations from numerous wells drilled at the same location (1).In theU.S., the first well drilled with synthetics that discharged the associatedcuttings occurred in 1993 (2) off Corpus Christi, TX.

Since this first use in the U.S., there have been a wide range ofenvironmental studies to understand the fate and effects of these discharges.The U.S. Environmental Protection Agency (EPA), the Department of Energy (DOE), and the Minerals Management Service (MMS) have all been supportive of thenumerous industry programs to develop real world data as it relates to U.S.drilling operations, and in some cases, have conducted their own studies.

In the mid–1990's when these studies were conducted, they were based on thesynthetic based fluids cuurently available (primarily polyalpha olefins andinternal olefins) and being used by operators in the U.S. Paraffins were notone of the readily available choices at that time.

Lacking international environmental standards for synthetic based muds, andbased in part on the numerous studies on the primary fluids being used in theU.S., the U.S. Environmental Protection Agency formulated a series ofenvironmental performance criteria which synthetic drilling fluids must meet inorder for the cuttings and associated muds to be discharge in U.S. waters.These requirements include toxicity testing of the base fluids and the wholemud, retention on cuttings limits for the adhered synthetic based mud (SBM), polycyclic aromatic hydrocarbon (PAH) level less than 0.001%, and adherence toa pass/fail criteria for biodegradation rates of the base fluids (based on ananaerobic test). The Environmental Protection Agency issued final effluentguidelines for the use of synthetic based muds in 1996(3).

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