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Collaborating Authors
Underbalanced Coiled Tubing Drilling Practices in a Deep, Low-Pressure Gas Reservoir
Kavanagh, Tom G. (Schlumberger) | Pruitt, Randal Dean (BP) | Reynolds, Mike (BP Sharjah) | Ortiz, Richard Angelini (BP plc) | Shotenski, Matt (Schlumberger) | Coe, Richard N. (Baker Oil Tools) | Davis, Paul (Halliburton) | Bergum, Roger (Halliburton)
Abstract The Sajaa field in Sharjah, United Arab Emirates, is a deep, low-pressure gas field that has been a prolific producer since the first wells were drilled in the 1980s. Initial field development was through a series of vertical wells drilled overbalanced with conventional drilling rigs. As field pressure and production declined, it became necessary to access additional reserves not being drained efficiently by these older wells. As a result of this need, a campaign to drill horizontal, multilateral sidetracks from the existing wellbores was started in March 2003 using coiled tubing. From a standpoint of production, cost, health, safety, and environment, the results of the program thus far have been excellent. This paper examines the surface and downhole equipment and operational best practices used in the Sajaa coiled tubing (CT) underbalanced drilling (UBD) campaign. It also reviews some of the key details that make a safer, more efficient day-to-day operation and created a highly successful project that has drilled 27 wells, comprising more than 90 laterals and more than 212,000 ft drilled. Introduction The Sajaa field was discovered in 1980 by Amoco Sharjah Oil Company; since that time a total of 41 wells have been drilled in the Sajaa field. Initial reservoir pressures were 7,500 psi or greater; these pressures have since declined substantially, with most wells now being drilled with equivalent circulating densities of 1.5 to 2.0 lb/gal. Initial completions were polished bore receptacle tubing completions, but with corrosion and packer leaks, these were changed to packerless 5-in. tubing completions with wells that have 7 -in. liners tied back and cemented to surface in most cases. Production trees are, for the most part, 5-31/8-in., 10,000-psi sour-service trees. The initial drive to perform CT UBD in this field came about because data on the Sajaa field showed that valuable reserves were not being added or produced, and that additional technology needed to be brought to this field to exploit these reserves. A peer-assist team composed of personnel from Alaska's North Slope, Houston Engineering Technical Practices (ETP), Sunbury, UK ETP, and Sharjah worked through the various options and found coiled tubing to be the best option. Downhole data transmission in underbalanced conditions can be done with pulse telemetry (previous UBD campaigns in Sharjah) or electromagnetic (EM) signals, but by 2003 the bottomhole pressure would not support a fluid column and the formations above the reservoir blocked EM transmission.
Abstract Amoco Sharjah Oil Company (ASOC) is conducting a horizontal/multi-lateral drilling program in the lower Cretaceous carbonate formation of its Sajaa retrograde/condensate field which lies at a true vertical depth of approximately -12,000 ft subsea. This program has included two single laterals and three dual lateral wells (two herringbone and a stacked-style). Three wells (one single and two dual laterals) were re-entries into original vertical development wells. Production rates from these wells are three to five times the calculated rate from vertical wells. Coil tubing production logging and stimulation operations were conducted in two of the wells of measured depth >15,600 ft (horizontal lateral length of 3,500 ft). Selective re-entry in the dual lateral with coil tubing was not successful. An acid wash stimulation improved the production rate by 30% in the single lateral well that was treated. The production log was capable of providing gross production rates of each lateral. A multilateral re-entry system has been installed in the current stacked-style dual lateral for future selective re-entry by coil tubing. Introduction Amoco Sharjah Oil Company discovered the Sajaa retrograde condensate field in December, 1980 and production began in 1982. The onshore Sajaa field is located in Sharjah, United Arab Emirates. The majority of the reserves have been developed from the Shuaiba and Kharaib carbonate formations in the lower Cretaceous Thamama group. The Shuaiba formation's top is at approximately -12,000 ft subsea and the Kharaib's top is 250 ft below the Shuaiba top. The Shuaiba is capped by the Nahr Umr shale formation. By November 1995 the field had been developed with 28 vertical development wells. A study concluded that a horizontal well in the Shuaiba should be significantly more productive than a vertical well because of wellbore contact increase. This led to the recommendation of the Sajaa field's first horizontal well. This paper reviews the drilling, completion and stimulation of the Sajaa horizontal wells; two single laterals and three dual laterals. The major drilling problem is geosteering in the Shuaiba formation because it has minimal logging characteristics, changing dip angles and unpredictable faults. The operations are complicated by the vertical depth of - 12,000 ft tvd and bottom hole temperatures of 295 F. The laterals are not lined, but the desire to selectively re-enter the dual laterals has led to several alterations in the completion philosophy. Completion designs have to be adapted to new wells and dual laterals which are initiated from original vertical wells. Coil tubing was used to run a production log in one of the dual laterals which allowed gross production measurement of each lateral. Selective re-entry into each lateral was not successful and the failed coil tubing acid stimulation required a work-over. The laterals were successfully re-entered with tubing and stimulated. Coil tubing was used to perform a 15% HCl acid wash of a single lateral increasing production by 30%. Horizontal Well No. 1 - Single Lateral The location of the first horizontal well was selected because the area had marginal productivity, but contained minimal reservoir uncertainties and dominant Shuaiba productivity. The well was drilled vertically to 10,490 ft then built to 390 at 11,478 ft (11,380 ft tvd) where the 9-5/8" casing was set in the Nahr Umr formation. An 8โ1/2" pilot hole was drilled through the target formation to define its characteristics. The porosity zone identified for the lateral was between 11,975 ft and 12,020 ft md (Fig. 1). It was bounded by the Nahr Umr shale (top) and Shuaiba low porosity (bottom). There was concern that the Nahr Umr shale below the 9-โ5/8" casing would be less stable at the higher inclinations so it was protected with a 7", 35 ppf liner. P. 349^
- Asia > Middle East > UAE > Sharjah > Oman Mountains Foldbelt Basin > Sajaa Field > Thamama Group Formation (0.99)
- Asia > Middle East > Qatar > Arabian Gulf > Rub' al Khali Basin > Idd El Shargi Field (0.99)
- Asia > Middle East > Oman > Central Oman > South Oman Salt Basin > Nahr Umr Formation (0.99)
- (7 more...)
Abstract This paper discusses underbalanced drilling planning, implementation and risk management to solve a drilling hazard where a weak upper formation is open to a lower high pressure gas reservoir that has pore pressure greater than the frac gradient of the weak formation. The problem has been solved in the Burgos Basin where loss of circulation and underground blowouts are a major hazard for drilling operations. The paper presents the planning process, risk assessment/HAZOP analysis, computer modeling with a steady state 2-phase flow model, equipment specifications, operational guidelines and field results from an underbalanced operation undertaken in August 2003 to successfully drill a well where there was a continual inflow while a weak lost circulation zone was exposed. Description and Results This paper documents a well drilled in the Burgos Basin where loss of circulation and underground blowouts are a major hazard. The well had suffered an underground blowout and a sidetrack was planned to recover the original hole and to reach the programmed well objectives. Risk assessments were performed which identified mitigations needed to minimize and control risk. Equipment design specification and installation were executed as per operational design for UBD. The operations maintained stable downhole pressure equilibrium of no losses or underground flows and the well successfully reached the original planned TD and completion requirements. Shown are the operational, risk assessment and field control guidelines used. The use of risk assessment, 2-phase flow calculations and operational guides are profiled for the operation. Lastly lessons learned are presented for safe and improved performance. Applications The principle idea was to use UBD techniques to solve difficult situations where the frac gradient of the open hole interval would not support a kill weight mud (e.g., the situation where kill weight mud looses circulation and lighter mud weight allows kicks and will flow underground if the well is shut in). In this situation UBD techniques saved the cost and complications of running additional contingency strings. Description of the Problem The Burgos basin is one of 4 major gas basins in Mexico. It is located on the western side of the Gulf of Mexico in the Mexican states of Tamaulipas and Nuevo Leon covering an area of 50,000 km and has about 1000 producing wells from 181 fields. The basin was discovered in 1945 and currently produces approximately 1.0 BSCF/D of non associated gas. The well where these techniques were employed was part of the Burgos Project in the La Cuenca de Burgos region. The reservoir is located in the north eastern part of Mexico, 60 kms from the Texas border. The geology is fairly consistent throughout the field and the Burgos Basin is considered a High pressure, High temperature environment located in Paleocene and Eocene formations. Since the formations are fairly young and naturally fractured there are many drilling hazards. Some of the unconsolidated intercalated weak sands are especially problematic when several gas bearing sands are crossed in the same hole section where losses and kicks occur simultaneously and there is no mud weight that will solve either problem successfully.
- North America > Mexico > Tamaulipas (1.00)
- North America > Mexico > Nuevo Leรณn (1.00)
- North America > United States > Texas (0.88)
- (2 more...)
- North America > Mexico > Tamaulipas > Burgos Basin (0.99)
- North America > Mexico > Nuevo Leon > Burgos Basin (0.99)
- North America > Mexico > Coahuila > Burgos Basin (0.99)
- Asia > Middle East > UAE > Sharjah > Oman Mountains Foldbelt Basin > Sajaa Field > Thamama Group Formation (0.99)
Introduction Located in the Emirate of Sharjah, United Arab Emirates, the Sajaa onshore gas field is a Thamama limestone reservoir ranging from 11,000 to 13,000 feet true vertical depth (3350 to 3960 meters true vertical depth). The bottomhole temperature is in the 260 to 310 degrees Farenheight (126 to 154 degrees Celcius) with bottomhole pressures of 1100 to 1900 psi (75 to 129 atmospheres). This paper will discuss the process used in basis of design, selection of bidders, pre tender qualifications, underbalance modeling, pre qualification, assurance testing of equipment, initial rig up, two phase nipple milling, window milling and the drilling of the first six wells in the Sajaa Underbalanced Coiled Tubing Drilling project. Background In April of 2002 a Production Technical Limit (PTL) meeting reviewed the wells and reservoir and identified the prize of unlocking additional permeability and height to gain additional rate and reserves. The PTL also identified the work required for sub surface evaluation of the reservoir with the basic questions of how much gas is left and where is the gas located. Idea's were then put forward on various options of snub drilling, conventional underbalance drilling as in the 2000 campaign, and coiled tubing drilling. All the options had one thing in common and that was the use of multi lateral wellbores to connect gas zones not fully connected with the vertical well mother bores. Coiled tubing drilling was evaluated as the best choice because of the need for real time directional steering where mud pulse is not possible due to the two phase fluids being pumped down the coil. In June of 2002 a Peer Assist was held in Sharjah with invited BP quests and distinquished underbalance/CTD/snubbing experts from Alaska, the North Sea, BP Houston's non conventional wells team, Service Company expertise from BP's experts in Colombia and underbalance consulting firms. The result of the three day meeting was a Risk Assessment with the Underbalance Coiled Tubing Drilling. Key areas of risk were:Personnel (right people, right skill sets, doing the right thing) High temperature equipment (300 degrees F assurance testing) Staffing levels identified (supervisory and operators) Two phase milling of nipples and windows Equipment availability Nitrogen (liquid versus membrane) Coil purchase, owner and lead-time Formation deliverability Loss of mother bore
- North America > United States (1.00)
- Asia > Middle East > UAE > Sharjah Emirate > Sharjah (0.47)
Abstract This paper describes the world's first true coiled tubing under balanced casing exit using a Nitrogen (N[2]) gas mist as the milling fluid, which allowed a well in Sharjah's Sajaa field to remain live throughout the casing exit, ensuring uninterrupted gas production. Previous attempts to mill a window using a N[2] gas mist with conventional milling technology proved unsuccessful. This was largely due to the lack of cooling and lubricity of the milling fluid resulting in a rapid deterioration of the window mills. Subsequent windows were milled using water only which resulted in massive fluid losses to the formation, due to the low reservoir pressures within the field, and more importantly caused interruptions to existing gas production. The technology described in this paper allowed gas production to be maintained throughout the window milling operation and resulted in a dramatic reduction in fluid losses to the formation and a reduction in overall casing exit time. Following the casing exit, the build and lateral drilling assemblies were deployed through the window at the first attempt, allowing uninterrupted progression to the under balanced drilling phase. This technology has helped to extend the life of the Sajaa field and secure the future of the Sharjah Coiled Tubing Drilling (CTD) project. Introduction The Sajaa onshore gas field is located in the United Arab Emirate of Sharjah and is operated by BP Sharjah and their partners. It is a low pressure (~1000psi) high temperature (300 F) reservoir, producing gas condensate from the Thamama limestone formation ranging from 11,000 to 13,000 feet true vertical depth. Gas production from the field was in rapid decline. Under balanced (UB) CTD was identified as the clear recovery solution and in April 2003 the Sharjah UB CTD campaign commenced. The objective being to sidetrack from the existing production casing and drill multi-lateral well bores into the reservoir to increase recovery rates. To date, 20 wells in the field have been sidetracked and over 230,000 feet of new well bore drilled, the majority being drilled under balanced. The gas produced from the Sajaa field is exported to the nearby Sajaa Gas Plant which generates electricity for the Emirate of Sharjah. For this reason it is critical that interruptions to the gas supply are minimized during the CTD operation. All drilling is performed using a N[2] gas mist of approximately 1500 cubic feet per minute of N[2] and 8 to 12 gallons per minute of water. Early attempts to mill the casing exit in a similar fashion using conventional window milling technology proved unsuccessful, largely due to the lack of cooling and lubricity from the milling fluid resulting in deterioration of the natural diamond window mill and an extremely low rate of penetration. This approach was abandoned and subsequent window milling operations were performed with water only resulting in a high volume of fluid loss to the formation due to the overbalanced condition created, interruptions to gas production and temporary production impairment. However, the risk to high rate gas producing wells was considered too great to continue in this manner and a gas milling solution was ultimately required to extend the scope of the CTD campaign.
- Well Drilling > Pressure Management (1.00)
- Well Drilling > Drilling Operations > Directional drilling (1.00)