Rheological properties of some oil based muds used in reservoirs in the Niger Delta, Nigeria
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 OBM3 and OBM2; 1st gel strength (8 -9 lb/ft2), 2nd gel strength (21 — 28 IbIft2), plastic viscosity (19-23 cP), yield point (6-23 Ib412) 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 (OBM5); 1st gel strength ( 171b1f12), 2nd gel strength (35 1b1112), plastic viscosity (49 cP), yield point (32 IbIft2) 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