Saudi Aramco attempted to drill horizontal deep gas carbonate wells without utilizing the Geo-steering technique in Hawiyah/ Uthmaniyah (HWYH/UTMN) field. In both 8-3/8" and 5-7/8" horizontal sections, much time was lost due to low ROP, sidetracks due to drilling in an unwanted pay zone and a stuck BHA, drilling with TCI and PDC bits (originally designed for vertical application).
A new approach was required to deal with this problem. The reservoir engineers and drilling engineers, together with service companies, analyzed each problem in detail and found the solution, utilizing LWD/Geo-steering technique. An improvement in casing design led to reduced MW across the pay zone. A geo-mechanical study was conducted and implemented its recommendation of drilling in the direction of maximum horizontal stress. This approach utilized PDC bits designed for horizontal drilling. This approach reduced drilling costs for over five laterals; compared to the previous five laterals in this carbonate reservoir (costs do not include the additional bits and pipe conveyed logging in these wells).
Utilizing the Geo-steering Technique in the carbonate reservoir increased the length of pay from 6,360 ft to 15,400 ft, an increase of 142% over a five-well average. It reduced the number of days required to drill five laterals from 364 days to 129 days, a reduction of 65%. Total lateral footage drilled for these five laterals reduced from 24,251 ft to 19,898 ft, a reduction of 18%. The average ROP improved over five wells from 6.11 ft/hr to 12.67 ft/hr. The average footage drilled per day increased from 66 ft/day to 154 ft/day and average number of bits used per well reduced from 13.4 bits to 3.6 bits per well. No sidetrack was required. One of the recent wells was drilled in record time for a HWYH/UTMN horizontal well and was also the longest single-lateral horizontal well in the field. One of the 8-3/8" PDC bits achieved record performance by drilling 4,475 ft in 261.5 hrs with an average ROP of 17.11 ft/hr, representing one of the longest intervals drilled by any 8-3/8" PDC bit in Khuff-C carbonate reservoir.