Shale Stickiness and Drill Bit Balling; Theory and Case Histories of Problems and Solutions in Louisiana and Gulf of Mexico

摘要

Whether a source of energy such as gas shale or a source of nuisance such as drill bit balling and slow drilling, the clay mineral content of Shale is a common thread running through many engineering and material science issues related to direct utilization of the earth or recovery of resources from the earth. Because of the stickiness of clay fraction in a fissile material such as Shale and its negative impact on drilling and hydraulic fracturing of gas shale, the author in this paper offers a theoretical approach based on Gibbs' Free Energy and a specific Hydration or Swelling Index for characterizing and classifying the shale as a material; For arriving at the free energy either we measure the enthalpy and entropy of the shale-clay material in a calorimeter directly or utilizing X-ray diffraction and X-ray fluorescence data from the shale samples obtained from various intervals to arrive at an accurate identification of shale-clay fraction and accurate oxide analysis of the shale-clay fraction. This data leads to writing the clay molecular formula. We present the final result in the form of a plot of Gibbs' Free Energy versus Hydration of Swelling Index. Here the calculation of Hydration or Swelling Index is based on the author's index, which is the natural log of the ratio of Oxygen to Hydroxyl contents of the shale-clay fraction (Ln k= [number of Oxygen, mol /number of Hydroxyl, mol]). To make the theory useful to the industry, the author has designed drilling fluid additives such as Modular Drilling Fluid System, MDFS, or additives for hydraulic fracturing fluids to counter or negate the shale-clay severity of "stickiness" or premature healing of the induced fractures. For example, the amount of additive to render the shale-clay "non-stick" is proportional to Gibbs' Free Energy and /or the total Hydration Index of the shale. Interestingly, in order to determine the concentration of additive in drilling fluid in a practical way, the author has correlated the proposed Hydration Index and the amount of additive needed to neutralize the shale-clay "stickiness" to the Neutron Log Porosity units and Gamma-ray Log Shale Index. More often than not the Neutron Porosity log indicates high porosity in shale with high "swelling or hydration" index. In order to validate this theory, the author has applied it to drilling more than two million ft of hole mainly in difficult Gulf Coast Shale sections. The success rate of this practice has been approximately 89 percent. We show some case histories of the application of theory in Mississippi Canyon (Offshore Gulf of Mexico) and in land operation in some of the 17 Parishes of Louisiana. Additionally the author presents correlation with some soil properties such as Plastic Index.