Relatively heavy crude production has historically been a problem in vertical completions in mature and new development fields in the Gulf of Mexico. Horizontal wells have been utilized to minimize water coning in potential completions that are close to the oil/water contact. However, horizontal completion costs are typically 60% more than vertical completions, consequently well and fluid design are critical to minimizing costs associated with drilling (fluid losses, wellbore stability, etc.).In addition to the engineering challenges for horizontal drilling, formulating a reservoir drill-in fluid (RDF) that minimizes invasion and fluid losses to the reservoir, provides compatibility between the reservoir fluids and the RDF fluid, and readily cleans-up is critical to success.

This paper will demonstrate the use of sidewall and conventional core material and subsequent petrophysical techniques to design a compatible RDF system. Core material from offset wells and previous vertical wells in several sands were utilized to develop bridging-material blends, determine sorting, texture, and particle and pore size.The authors discuss the advantages and disadvantages of using this type of material as well as that of a relatively new computer technique that allows a pore-size distribution to be rapidly calculated from core material.Another technique utilizes the rock attributes and log information in conjunction with a rock catalog to facilitate rapid determination from analogs. This type of data, in turn, can ultimately be utilized to design an RDF system.As such, this method will also be described and contrasted with traditional methods.

Finally, case histories from several recently drilled horizontal wells that incorporated the subsequent RDF bridging-solids design using the aforementioned techniques will be presented. Fluid losses and solids loading will be examined with respect to the RDF designs.

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