Experimental Measurements of the Capillary Entry Pressure of Outcrop and Field Shale

Abstract

The oil industry often faces borehole stability issues when drilling through shale, especially shale that is water-wet. It is often observed that drilling with oil-based mud yields the best results due to the capillary forces between oil and water, which enable the wellbore pressure to be higher than the pore pressure of the formation. If, however, the wellbore pressure exceeds the pore pressure by a certain amount, the capillary forces will be overcome and drilling fluid will enter the formation. This can lead to borehole instability, thus making the capillary entry pressure of various types of shale of interest to the industry. In this thesis, test procedures to determine the capillary entry pressure of shale were examined. The capillary entry pressure of Pierre I shale was measured to be 0.57 MPa when subjected to a mineral oil. The results for the field shale tested in regards to this thesis were not satisfactory. The test procedure was in the end considered a success, but the suitability of the methods used for this thesis needs to be determined for additional shale types.