Coiled-Tubing-Conveyed Perforating for Maximizing Underbalanced in Hard Rock
Abstract: This paper describes a variety of Coiled Tubing perforating approaches and techniques which have been evaluated, planned and implemented during the development of the Cusiana and Cupiagua Fields. A synopsis has also been prepared which outlines the advantages/disadvantages of each of these approaches. In addition, several detailed case-histories are included which provide the actual Operating characteristics of each approach. The particular operational advantages, of Coiled Tubing Perforating… Show more
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Cited by 6 publications
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The transition from completion to production often requires the well to be killed immediately after perforation is completed, thus exposing the formation to potentially damaging kill fluid. To obtain a perforation tunnel with maximum productivity, this transition requires an optimal cleanup and the removal of the perforation damages. A new underbalanced oriented perforating technique has been successfully implemented in Algeria. It combines the use of a formation isolation valve (FIV) to keep damaging completion fluid off the formation immediately after perforation and a perforating technique that utilizes the dynamic underbalanced method, which cleans perforations with more efficiency than conventional static underbalanced perforating method. In addition, a passive gun-orienting system was used to optimize the perforating process and enhance the well's performance. The new technique was applied in 2003 to horizontal Well-1, which was drilled by in the Tadrart sandstone formation of the Berkine basin. After successful results in this well, the operator adopted its use in 2005 for two additional wells, Well-2 and Well-3. The paper describes the application of the new technique to three horizontal wells of the Berkine basin and the evaluation of the related productivity increase vs. the conventional perforating method. Introduction In 1981, the operator started its exploration activity in block 403 of Algeria. The area is located in the Berkin basin, on the Sahara platform and close to the Tunisian border as shown in Fig. 1. In the same area, several important oil discoveries including Rhourde Messaoud, Bir Rebaa North, Bir Rebaa West, and Bir Rebaa South West were made between 1981 and 1995. The geological features in this region are characterized by two main fault systems: one main fault system that runs parallel to the northeast-southwest El Bourma regional fault, and a second system having a northwest-southeast direction. These systems were probably generated during the Ercynian phase and were reactivated during the Mesozoic period to generate the actual structural setup. The anticlinal oil-bearing structures in this area are elongated in a north-northeast-south-southwest direction and bounded toward the west and south by the two main normal fault systems. Field-a was discovered in 1986 with evidence of hydrocarbons in the Tadrart sandstone formation (Lower Devonian/Gedinian), which is one of the main reservoirs of this field. Field-ß was discovered in 2002. It is located in the western sector of block 403 at a distance of 25 km west from Field-a. In this area, the Tadrart formation underlies directly below the hercynian unconformity (Fig. 2), which confirms the progressive erosion of the Devonian stratigraphic succession towards the east-northeast direction. The petrophysical characteristics of the Tadrart sandstone are good with porosity ranging between 12 to 16%; the permeability is in the order of 100–200 md. The reservoir properties are quite homogeneous over the field, thus providing optimum candidate wells for the initial evaluation of the new perforating technique. Background Well-0 was the discovery well of Field-ß. It was drilled as a vertical well and completed with a standard completion including a 3.5-in. production tubing and a 7-in. packer. Well-0 was perforated in static underbalanced conditions and tested at 334 standard cubic meters per day (Sm3/d). In May 2003, the operator started the drilling phase of Well-1, located 800 m west from Well-0. The original objective of Well-1 was to appraise the field after the Well-0 discovery. The decision to drill Well-1 as a horizontal well at the top of reservoir was motivated by the possibility of obtaining a higher production rate than Well-0.
The transition from completion to production often requires the well to be killed immediately after perforation is completed, thus exposing the formation to potentially damaging kill fluid. To obtain a perforation tunnel with maximum productivity, this transition requires an optimal cleanup and the removal of the perforation damages. A new underbalanced oriented perforating technique has been successfully implemented in Algeria. It combines the use of a formation isolation valve (FIV) to keep damaging completion fluid off the formation immediately after perforation and a perforating technique that utilizes the dynamic underbalanced method, which cleans perforations with more efficiency than conventional static underbalanced perforating method. In addition, a passive gun-orienting system was used to optimize the perforating process and enhance the well's performance. The new technique was applied in 2003 to horizontal Well-1, which was drilled by in the Tadrart sandstone formation of the Berkine basin. After successful results in this well, the operator adopted its use in 2005 for two additional wells, Well-2 and Well-3. The paper describes the application of the new technique to three horizontal wells of the Berkine basin and the evaluation of the related productivity increase vs. the conventional perforating method. Introduction In 1981, the operator started its exploration activity in block 403 of Algeria. The area is located in the Berkin basin, on the Sahara platform and close to the Tunisian border as shown in Fig. 1. In the same area, several important oil discoveries including Rhourde Messaoud, Bir Rebaa North, Bir Rebaa West, and Bir Rebaa South West were made between 1981 and 1995. The geological features in this region are characterized by two main fault systems: one main fault system that runs parallel to the northeast-southwest El Bourma regional fault, and a second system having a northwest-southeast direction. These systems were probably generated during the Ercynian phase and were reactivated during the Mesozoic period to generate the actual structural setup. The anticlinal oil-bearing structures in this area are elongated in a north-northeast-south-southwest direction and bounded toward the west and south by the two main normal fault systems. Field-a was discovered in 1986 with evidence of hydrocarbons in the Tadrart sandstone formation (Lower Devonian/Gedinian), which is one of the main reservoirs of this field. Field-ß was discovered in 2002. It is located in the western sector of block 403 at a distance of 25 km west from Field-a. In this area, the Tadrart formation underlies directly below the hercynian unconformity (Fig. 2), which confirms the progressive erosion of the Devonian stratigraphic succession towards the east-northeast direction. The petrophysical characteristics of the Tadrart sandstone are good with porosity ranging between 12 to 16%; the permeability is in the order of 100–200 md. The reservoir properties are quite homogeneous over the field, thus providing optimum candidate wells for the initial evaluation of the new perforating technique. Background Well-0 was the discovery well of Field-ß. It was drilled as a vertical well and completed with a standard completion including a 3.5-in. production tubing and a 7-in. packer. Well-0 was perforated in static underbalanced conditions and tested at 334 standard cubic meters per day (Sm3/d). In May 2003, the operator started the drilling phase of Well-1, located 800 m west from Well-0. The original objective of Well-1 was to appraise the field after the Well-0 discovery. The decision to drill Well-1 as a horizontal well at the top of reservoir was motivated by the possibility of obtaining a higher production rate than Well-0.
In the Bay of Campeche, Mexico Marine operators have recently commenced the development of their high pressure, high temperature (HPHT) oil and gas fields in order to meet the high demand. These new developments present tough conditions for all aspects of well drilling and completion activities. They are particularly challenging for performing well intervention, which have driven operators, manufacturing and service companies to develop innovative strategies for servicing these fields. For HPHT well developments, electric line conveyed guns is the most common technique employed to perforate wells in the area, whether dynamic or static conditions. Nevertheless, coiled tubing (CT) deployed perforating has been recently employed as a reliable option in the following cases:Electric line is not a technically suitable option due to the limited magnitude of under-balance at which it can safely operate.Drag and buoyancy forces encountered in the wellbore are close to the operational limits of the cable.Wellbore tortuosity, tubular restrictions and well configuration render electric line unable to access perforation target depth. Initially, this paper discusses the workflow for performing technical analysis to develop safe and economical CT conveyed perforating operations for HPHT wells in offshore Mexico, which considers CT string design, surface equipment, well control equipment and associated downhole tools. It then presents case histories and lessons learned. And finally, provides conclusions and recommendations from the experiences gained for performing HPHT CT deployed perforating activities in Mexico Marine. Introduction HPHT define well conditions above what is considered normal levels of pressure and temperature. For Mexico Marine operators any well intervention with wellhead pressure (WHP) above 3,500 psi and bottomhole temperature over 150 oC (BHT) is considered HPHT. The Bay of Campeche is located at the southeast of Mexico in the continental platform of the Gulf of Mexico in front of Tabasco, Campeche and Yucatan coasts (Fig. 1). In 2004 Mexico Marine operators started to develop in the Bay of Campeche a significant number of fields that meet HPHT definition. In Mexico Marine HPHT fields, electric line conveyed gun is the most common technique employed to perforate wells. However, CT conveyed perforating has been recently proved as an excellent option in cases where electric line restricts under-balance magnitude for safe operation, drag and buoyancy forces encountered in the wellbore are close to the operational limits of the cable, and tubular restrictions and well configurations may be a concern to access perforation target depth. Mexico Marine HPHT Environment HPHT developments (Fig. 2) in the Bay of Campeche target Cretaceous (K) and Upper Jurassic Kimmeridgian (UJK) formations. Cretaceous is a naturally fractured carbonate formation ranging depths from 4,500 to 5,500 m with Porosity ranges from 3.0 to 5.0% and Permeability of 18 md. Upper Jurassic Kimmeridgian is a dolomitized carbonate formation in Oolitic banks from 5,000 to 6,000 m, where Porosity ranges 5.0 to 8.0% with Permeability from 20 to 40 md. The new fields under development are highly pressurized with bottomhole pressure (BHP) from 10,000 to 12,000 psi and BHT up to 190 oC. In surface, shut-in pressures from 6,000 to 8,500 psi have been recorded, and hydrocarbon production is composed by gas and oil from 27.0 to 48.0 oAPI. Drilling operations are performed by jackup rigs from eight-leg fixed platforms in water depths up to 60 m. Well deviation ranges 0 to 60 o, and jackup rigs are also the most common structures available for well completion and workover operations. These rigs have a limited crane capacity of 30 ton to lift and position CT string onboard.
A perforating job conveyed with electric coiled tubing (CT) was recently completed in a high angle well offshore in the UAE using a combination of several new technologies which allowed this job to be completed safely and efficiently. Perforating operations with electric coiled tubing in offshore environments with restricted space have been considered hazardous and were avoided in the past because of the requirement to connect and finally arm the gun system while working at the wellhead below the coiled tubing injection head and other heavy equipment. Following the old standard operating procedures for explosive operations, arming the gun with the explosive detonator had to be done after the electric coiled tubing head was attached to the gun string. This gun arming activity is potentially hazardous as the work is being done in a tight space below very heavy equipment hung off on a crane line. Jobs using these old operating procedures were often cancelled as the potential risk to personnel and equipment was deemed to be too high. Also the length of perforating gun that could be run in one trip was severely limited by these procedures. Recently several new perforating gun and deployment technologies have been introduced to the field that make the electric CT perforating technique much more efficient and safe compared to past operations. These technologies includeA new expendable electronic addressable switch device providing electrical control and a safety barrier to each detonatorA simplified radio safe detonator which incorporates several intrinsic safety featuresAn electric deployment bar for perforating used to deploy the guns into a live well before the electric CT is connected. In addition to the above, a CT intervention was optimized to accomplish several tasks as part of the same offshore barge visit for a rigless intervention in a producing well with one CT rig-up. In addition to the perforation runs, CT was run to acid stimulate both existing zones and the newly perforated zone in the well. CT was also used to convey production logging tools to measure the production characteristics along the entire deviated section. This paper will describe how the combination of these new and existing technologies contributed to a safe coiled tubing perforating operation, improved overall efficiency and improved production from the well. There are many opportunities worldwide for perforating with electric coiled tubing and the application of these new technologies will enable more of these jobs to be attempted and to be completed safely and efficiently. Introduction Coiled tubing (CT) is being used more and more to convey tools and perforating guns into wells where it is required to maintain wellhead pressure control and push equipment into highly deviated or horizontal sections or carry heavier loads than a wireline system can handle1. Another advantage of CT conveyance is the ability to pump fluids into the well as part of the conveyance operation. Over the past few years more and more CT equipment is being fitted with electric logging cable (e-line CT) to replicate the features available with electric wireline operations, mainly surface readout of tool measurements and, in the case of perforating, being able to establish accurate depth control, fire the guns using electric detonators and using switches to shoot perforating guns selectively.
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