Rheological properties of some oil based muds used in reservoirs in the Niger Delta, Nigeria

M.C Onojake,T.N Chikwe

doi:10.4314/gjpas.v25i1.6

Abstract

Rheological properties of some oil based muds used in oil reservoirs located in the Niger Delta area of Nigeria were analyzed using standard methods (American standard for testing and material. Rheological parameters were obtained with a rotational viscometer by relating the shear stress of the fluid to the shear rate of the equipment. Results obtained from two of the oil based muds labelled OBM 3 and OBM 2 ; 1st gel strength (8 -9 lb/ft 2 ), 2nd gel strength (21 — 28 IbIft 2 ), plastic viscosity (19-23 cP), yield point (6-23 Ib41 2 ) show that the properties were within mud specification as recommended by American Association of Drilling Engineers (AADE) while results from the third oil based mud (OBM 5 ); 1st gel strength ( 171b1f1 2 ), 2 nd gel strength (35 1b111 2 ), plastic viscosity (49 cP), yield point (32 IbIft 2 ) show that the parameters were off mud specification. Plastic viscosity and yield points are flow parameters of drilling fluids determined by their solid concentration and electrochemical forces within the particles of the fluid respectively whereas the gel strengths are time dependent flow parameters hence they are termed thixotropic. Rheological properties maintained within mud specification as specified by AADE are essential for efficient drilling operations. Keywords: Newtonian, Thixotropy, Shear Stress, Shear Rate, Organophillic, Flocculation

Highlights

Hydrocarbons beneath the earth crust are globally recovered from reservoirs through a process of drilling with the aid of “complex heterogeneous fluids” known as drilling fluids
All the rheological parameters were measured in Ib/100ft2 except the plastic viscosity which is measured in centipoise. 1st and 2nd gel strengths are measured at 10 seconds and 10 minutes respectively
For non Newtonian model no linear constant proportionality exists between the shear rate and the shear stress, the viscosity changes as the shear rate changes

Summary

Introduction

Hydrocarbons beneath the earth crust are globally recovered from reservoirs through a process of drilling with the aid of “complex heterogeneous fluids” known as drilling fluids. Drilling fluids play a significant role in aiding the drilling of borehole into the earth (Bourgoyne et al, 1986). The Egyptian and Chinese cultures used water as the first drilling fluid (Barrett, 2011). The major roles of drilling fluids during drilling operations include provision of gravitational pressure which prevents reservoir fluids from entering into the uncased portion of the well, ensuring that the cleanliness and temperature of the drill bit during drilling operations are maintained and aiding the adequate handling of broken bits of solid materials while drilling apparatus is brought in and out of the well bore during intermittent suspension of drilling activities (Darley and Grey, 1988). Some drilling activities require specific drilling fluid at a particular part of the hole others require a combination of different fluids (Barrett, 2011)

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Conclusion