Abstract

Saudi Aramco attempted to drill horizontal deep gas Carbonate 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, muchlong time was spentlost due to low ROP, sidetracks due to drilling in an unwanted pay zone / and a stuck BHA, drilling with TCI or and vertical application PDC bits (originally designed for vertical application).

A nNew approach was required to deal with this problem. The reservoir engineers and drilling engineers, together with service companies, approached these wells with a different dimension. analyzed eEach problem was analyzed in detail and solvedfound the solution, utilizing LWD/Geo-steering technique., An improvement in casing design led to reduced MW across the pay zone,. A Ggeo-mechanical study was conducted and implemented its recommendation of drilling in the direction of maximum horizontal stress., This approach utilized utilizedadvanced technology PDC bits designed for horizontal drilling., This approach reducinged drilling costs for over drilling five laterals; compared to the previous five laterals in this carbonate reservoir by over US$ 7.28 million (costs do not include the of additional bits and pipe conveyed logging in these wells in the lateral section of five wells drilled without the use of geosteering technique is not considered for simplicity).

Utilizing the Geo-steering Technique in these 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 Hawiyah / Uthmaniyah 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.

Introduction

Saudi Arabia is best known as the world's largest oil producer averaging 8.1 million barrels per day and for having the world's largest oil reserves (259.4 billion barrels as of 2003 year end). The Kingdom also holds the world's fourth largest natural gas reserves of 234.5 trillion standard cubic feet and produces 6.9 billion standard cubic feet per day of non- associated gas1.

Saudi Aramco began a major non-associated gas expansion program in the 1990's. This program added 55 trillion standard cubic feet of non-associated gas reserves. Most of the produced gas is in the form of sales gas (a mixture of methane and ethane) and is sold to domestic customers as fuel and petrochemical feedstock.

To meet the forecasted domestic gas demand of 12 billion standard cubic feet per day (bscfd) by 2025, Saudi Aramco is accelerating its deep gas well development and exploration drilling campaign in the Khuff and Pre-Khuff formations.Saudi Aramco currently operates 46 drilling rigs for both onshore and offshore operations, out of which 13 are deep onshore drilling rigs for Khuff and Pre-Khuff gas well development and exploration wells. Four more deep drilling rigs are being added in 2005 for drilling gas wells. Moreover, Saudi Aramco has signed four extensive gas exploration and development agreements in the Rub' al-Khali basin with Sinopec, Lukoil, and two consortiums i.e:. Shell & Total, and ENI & Repsol YPF.

Economic importance of Khuff reservoirs

The Khuff reservoirs are responsible for approximately 75% of Saudi Aramco's current 6.9 bscfd of non-associated gas production. Practically all of the gas produced in Khuff comes from Khuff-A, Khuff-B and Khuff-C reservoirs with Khuff-C being the most prolific.

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