Drilling horizontal wells is a common practice for Saudi ARAMCO in most of its oil and gas reservoirs of Saudi Arabian clastic and carbonate fields. A comprehensive study of rock mechanical properties with detailed analysis of the in-situ stress field was conducted to evaluate well stability during drilling and completion across a friable eolian oil-bearing sandstone reservoir. This paper discusses the application and implementation of the study to successfully drill and complete development horizontal wells in a challenging sandstone reservoir.

All horizontal wells were completed with different type of sand screens including Premium and Expandable Sand Screen (ESS). It is vital to obtain a near-gauge hole during drilling for a maximum stability of the screen during the life of a well. It is therefore important to prevent excessive compressive shear failure at the wellbore wall and avoid instability problems during drilling and completion. Therefore, an optimum confining pressure to the wellbore surface needs has been derived. The recommended mud type and weight windows derived from the study have been employed while drilling producers but not with injectors. The correlation between the mud weights and the in-situ stress magnitude will be discussed.

Well stability during drilling and long term screen integrity is dependant on the well azimuth relative to the in-situ stress field. The azimuth of the maximum horizontal stress, SHmax, was determined to generally line up in the E-W direction. The wellbore stability problems experienced in this direction as well as those drilled normal to it (i.e., N-S), will be addressed.

In regards to stability of very weak and friable formation intervals (such as those encountered in the, dunes and sand sheet facies), the operational practices are focused on creating gauged hole with least erosion effect as a critical measure to deploy the ESS; thus, ensuring successful completion and sustained production. The effect of mud on rock strength was evaluated during the foregoing study; therefore, results from using oil-base mud will be discussed and compared to results from the wells drilled with water-based mud.

Keywords:
Directional Drilling, strength, mud weight, wellbore integrity, Wellbore Design, drilling fluids and materials, Sandstone Reservoir, Upstream Oil & Gas, completion, Reservoir Characterization
Subjects:
Wellbore Design, Drilling Operations, Drilling Fluids and Materials, Reservoir Characterization, Wellbore integrity
Copyright 2009, Society of Petroleum Engineers
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