Borehole stability problems persistently remain the bane of drilling operation in the oil and gas industry. It is imperative to understand the drilling fluid properties that contribute to these problems. The effects of mud cake build-up and filtration with time support the understanding of formation damage and wellbore stability. The increase of drilling in High Pressure High Temperature zones (HPHT) compels studies that can predict filtrate invasion and particle bridging. Very few studies have investigated filtration and filter cake formation under HPHT situations where the effect of different mud particles and bridging solids can be analyzed.
This study focuses on experimental methods quantifying wellbore strengthening effects in oil based muds used by the industry and investigating effects on particle bridging, filtrate invasion and permeability. A unique image analysis technique is used to optimize Particle Size Distribution (PSD) for wellbore strengthening’s pill design. To show the particle bridging effect, HPHT filtration tests were conducted at different time steps on four actual sandstone cores with permeability ranging from 15.9 md to 1130 md. Further rock cores and mud cakes were analyzed using Scanning Electron Microscopy (SEM) to verify bridging efficiency.
The study concludes a significant reduction in cumulative fluid loss (up to 100 % in some cases). Low mud cake permeabilities in the range 10 -2 to 10-3 milliDarcy that can be very beneficial for wellbore strengthening applications was produced. Optimized particle size distribution of LCMs yielded an effective bridging of core samples pore spaces. Ultra-thin and firm mud cake was formed which can prevent differential sticking, excessive drag, and torque on drill pipes. Further filtration studies are in progress using other LCM types and concentrations as well as field test verification.
|Commitee:||Guo, Boyun, Hayatdavoudi, Asadollah|
|School:||University of Louisiana at Lafayette|
|School Location:||United States -- Louisiana|
|Source:||MAI 54/06M(E), Masters Abstracts International|
|Keywords:||Filtrate characterization, Mud cake, Non-aqueous drilling fluids|
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