Improved drilling techniques have overcome many of the inherent difficulties associated with the delivery of Icotea and Misoa wells in the West Urdaneta Field of Lake Maracaibo. Advancements such as rotary steerable assemblies, logging-while-drilling (LWD) tools, annular pressure subs and new bit designs have allowed drilling of extended reach and horizontal wells to become routine. However, borehole instability and lost circulation problems have continued to negatively impact operations, compounding well delivery costs.
In an effort to address these problems, a variety of non-aqueous fluids (NAF) and water-based muds (WBM) have been used. While each provides distinct advantages, there has never been a system which could solve all problems associated with drilling the Icotea and Misoa formations. Lost circulation and wellbore instability (defined by almost continual caving of shales in the La Rosa formation) have plagued NAF applications in this field. A variety of WBM systems have been used and each one has also presented its own problems including hole enlargement, bit balling, accretion, low rates of penetration, insufficient hole cleaning, and the need for excessive backreaming.
Finding a fluid that would deliver step-change performance in of drilling efficiency compared to previously used systems, while also adhering to the strict environmental limitations for the area, was paramount to continue economically viable drilling operations in the Urdaneta Field. This challenge was met using an environmentally benign, low-salinity high-performance water-based mud (HPWBM), which was field tested in the intermediate section of the Icotea and Misoa wells. The novel fluid was used to drill through the problematic Laguna, Lagunillas, and La Rosa formations.
By analyzing the field tests results, conducting after action reviews (AAR) and maintaining a productive dialogue between all parties involved, the operational performance of these wells showed substantial and continual improvement. The low-salinity HPWBM is now our system of choice for drilling intermediate hole sections in the West Urdaneta Field.
This paper provides a detailed technical overview of the new HPWBM, provides and the results of the early field tests and of subsequent wells, demonstrates enabling impact of this new technology on driving continual operational improvement.
Introduction
As the search for new oil and gas reserves continues, operators are increasingly moving towards drilling more challenging well trajectories. The search for new oil reserves has also led operators into more remote and environmentally sensitive areas. Drilling in these areas, especially with complex well designs, presents considerable technical, economical, and environmental risks and challenges.
The intermediate sections of West Urdaneta wells have been drilled with a wide variety of WBM systems since the first well was drilled in 2001. Dispersed WBM, at first, yielded high rates of penetration (ROP) However, these systems were plagued by excessive hole enlargement, clay instability, problematic trips, pack-off and lost circulation events. More inhibitive WBM's were tried and while these systems produced satisfactory clay- and shale stability, problems arose from accretion and associated ROP reduction.
Finally, attempts were made to improve fluid performance through use of NAF. The continual generation of cavings (creating problems with hole cleaning, and tripping pipe) and catastrophic lost circulation events that occurred with these fluids more than negated the benefits they provided with respect to reducing accretion and increasing ROP.
Legislation to control the use and discharge of cuttings and spent fluid in Lake Maracaibo area is becoming more stringent. The Venezuela Ministry of the Environment has developed legislation to minimize the impact of drilling activities by eliminating discharges to Lake Maracaibo, not only of NAF, but also of the high salinity WBM.
