TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn the moderate-permeability environment of the Hassi Messaoud field of central Algeria, proppant fracturing has significantly increased production, prolonging the economic life of many wells. Unfortunately, the logistics of mobilizing a workover rig to prepare the wellbore for stimulation has extended the stimulation cycle time. Additionally, many wells have tubular problems that require intervention such as squeeze cementing or tubular replacement before the stimulation process can begin. The availability of coiledtubing equipment in the field provides the means to stimulate the wells without a workover rig. Furthermore, when coupled with a mechanical isolation system, the coiled-tubing fracturing technique protects the production tubing from high treating pressure and abrasive proppants. In the past, the lack of a reliable isolation system has limited the success of these jobs.Reservoir conditions throughout the field allow low-rate stimulations but induce high bottomhole pressures, which make the use of conventional packers difficult. In many environments the bottomhole treating pressure creates differential pressures across the elements of a packer in excess of 9,000 psi. Several attempts to use existing packer technology yielded unsuccessful fracture treatments, and costly fishing operations were necessary to restore the wells to production. To provide an economical solution to the problems encountered by conventional mechanical packers, a new isolation system was designed. This paper provides case histories of several wells stimulated with coiled-tubing fracturing in the extreme environment of high-pressure, deep wells in the Hassi Messaoud field and examines the engineering challenges in developing a robust isolation system.
The Hassi Messaoud field (Figure 1), discovered in 1956, is the largest oil field in Algeria, covering about 2000 Km2 and currently including over 1000 Wells. The field is divided aerially into 25 zones that are separated from each other by low permeability barriers, usually faults. The Cambrian Reservoir is subdivided into four lithological zones designated from base to top as R3, R2, Ra and Ri. The Ra sub reservoir shows the best petrophysical properties with a maximum thickness of 150 m in the western part of the field. The Ra is farther subdivided into five sub zones: D1, ID, D2, D3, and D4 based on reservoir properties and depositional conditions. Well F was the 6th re-entry well in the Sonatrach Coiled Tubing - Underbalanced Drilling campaign. A total of 363 m from KOP (303 m from landing point) were successfully drilled in a continuous underbalanced condition inside D1 and ID formations. As a result, the well productivity while drilling and while production test, the reservoir characterization and rate of penetration was significantly improved, compared with offset wells, due to the positive impacts of UBD operations. The combination of Underbalanced and Coiled Tubing Drilling technologies has been proven to be a viable solution to successfully drill horizontal re-entry wells in mature fields where the reservoir pressure is adequate to induce underbalanced conditions using single phase or multiphase drilling fluid. The experience in this field has validated the benefits of the combination of these technologies and has been attributed to the excellent balance between drilling cost and improved productivity. For example, the drilling cost in the short radius re-entry wells drilled with coiled tubing are highly reduced due to the elimination of pipe connection procedures, the increase in rate of penetration, the prevention of conventional drilling problems such as fluid circulation loses and related differential sticking events, the increase in the bit life and reduction in time and drilled distance to reach the profitable production level. This paper describes the technical basis for the design and implementation of the Coiled Tubing Underbalanced Drilling project in Hassi Messaoud Field and highlights the operational key factors and challenges faced during this particular and successful application in Algeria. Introduction Drilling in the Cambrian Reservoir, in the peripheral zone of Hassi Messaoud field, specifically the 1A, 1B and 1C zones (Figure 2) is a real challenge, basically due the petrophysical reservoir complexity, the low reservoir pressure, the extremely hard and abrasive sandstone and quartzite formation (15000 - 35000 psi UCS) associated with numerous vertical and sub vertical fractures that connect the reservoir with deeper formations leading to major problems related with the salt saturated water production. Many of the vertical wells drilled in that zones have more than 30 years from completed and a large proportion of them have been shut in since being drilled. This is the first of its kind Coiled Tubing - Underbalanced Drilling project undertaken in Hassi Messaoud field. The candidates wells are from a pool of vertical shut in wells drilled in the western area of the field and have seized to produce with varying completion string and production casing. The increase in number of candidates for thru tubing re-entries added to the depletion of the reservoir have raised the importance of use the combined technologies Coiled Tubing - Underbalanced drilling in Hassi Messaoud field. The original reservoir pressure was 6860 psi and the average permeability ranges from 0.5 to 1.0 mD but can reach up to 1000 mD in cases where open fractures are encountered. Production is 43.7 - 45 º API oil with original average GOR of about 200 m3/m3 and a formation temperature of approximately 120 ºC. Until 1964, the production mechanism was only depletion above bubble point. Gas injection and water injection started after that year to improve the production.
The Hassi Messaoud field (Figure 1), discovered in 1956, is the largest oil field in Algeria, covering about 2000 Km2 and currently including over 1000 Wells. The field is divided aerially into 25 zones that are separated from each other by low permeability barriers, usually faults. The Cambrian Reservoir is subdivided into four lithological zones designated from base to top as R3, R2, Ra and Ri. The Ra sub reservoir shows the best petrophysical properties with a maximum thickness of 150 m in the western part of the field. The Ra is farther subdivided into five subzones: D1, ID, D2, D3, and D4 based on reservoir properties and depositional conditions. Well MD-330 was the 4th re-entry well in the Sonatrach campaign. A total of 330 m from landing point were successfully drilled in a continuous underbalanced condition inside D4. As a result, the well productivity was significantly improved, compared with offset wells, due to one of the positive impacts of UBD operations, namely that of the elimination of formation damage. The combination of Underbalanced and Coiled Tubing Drilling technologies has been proven to be a viable solution to successfully drill horizontal re-entry wells in mature fields where the reservoir pressure is adequate to induce underbalanced conditions using a single phase drilling fluid. The experience in this field has validated the benefits of the combination of these technologies and has been attributed to the excellent balance between drilling cost and improved productivity. For example, the drilling cost in the short radius re-entry wells drilled with coiled tubing are highly reduced due to the elimination of pipe connection procedures, the increase in rate of penetration, the prevention of conventional drilling problems such as fluid circulation loses and related differential sticking events, the increase in the bit life and reduction in time and drilled distance to reach the production zone. This paper describes the technical basis for the design and implementation of the Coiled Tubing Underbalanced Drilling project in Hassi Messaoud and highlights the operational key factors and challenges faced during this successful application in Algeria. Introduction Drilling in the Cambrian Reservoir, in the peripheral zone of Hassi Messaoud field, specifically the 1A, 1B and 1C zones (Figure 2) is a real challenge, basically due the petrophysical reservoir complexity, the low reservoir pressure, the extremely hard and abrasive formation associated with numerous vertical and subvertical fractures that connect the reservoir with deeper formations leading to major problems related with the salt saturated water production. Many of the vertical wells drilled in that zones have more than 30 years of production history, a large number of them are closed due suffering from severe corrosion. This is the first of its kind Coiled Tubing - Underbalaned Drilling project undertaken in Hassi Messaoud field. The candidate wells are from a pool of vertical wells drilled in the western area of the field and have ceased to produce with varying completion strings and production casing. The increase in number of candidates for slim hole re-entries added to the depletion of the reservoir have raised the importance of using the combined Coiled Tubing - Underalanced drilling technologies in Hassi Messaoud field. The original reservoir pressure was 6860 psi and the average permeability ranges from 0.5 to 1.0 md but can reach up to 1000 md in cases where open fractures are encountered. Production is 43.7 - 45 º API oil with original average GOR of about 200 m3/m3 and a formation temperature of approximately 120 ºC. Until 1964, the production mechanism was only depletion above bubble point. Gas injection and water injection started after that year to improve the production.
Drilling in the Cambrian Reservoir, in the peripheral zone of Hassi Messaoud field, specifically the 1A, 1B and 1C zones (Figure 1) is a real challenge, basically due the petrophysical reservoir complexity, the low reservoir pressure, the extremely hard and abrasive sandstone and quartzite formation associated with numerous vertical and sub vertical fractures that connect the reservoir with deeper formations leading to major problems related with the salt saturated water production. Many of the vertical wells drilled in that zones have more than 30 years from completed and a large proportion of them have been shut in since being drilled. Well E was the 5th re-entry well in the Sonatrach Coiled Tubing - Underbalanced Drilling campaign. A total of 372 m from KOP and 316 m from landing point were successfully drilled in a continuous underbalanced condition inside D1 formation. As a result, the well productivity while drilling, the Reservoir characterization and rate of penetration was significantly improved, compared with offset wells, due to the positive impacts of UBD operations. The combination of Underbalanced and Coiled Tubing Drilling technologies has been proven to be a viable solution to successfully drill horizontal re-entry wells in mature fields where the reservoir pressure is adequate to induce underbalanced conditions using single phase or multiphase drilling fluid. The experience in this field has validated the benefits of the combination of these technologies and has been attributed to the excellent balance between drilling cost and improved productivity. For example, the drilling cost in the short radius re-entry wells drilled with coiled tubing are highly reduced due to the elimination of pipe connection procedures, the increase in rate of penetration, the prevention of conventional drilling problems such as fluid circulation loses and related differential sticking events, the increase in the bit life and reduction in time and drilled distance to reach the profitable production level. This paper describes the technical basis for the design and implementation of the Coiled Tubing Underbalanced Drilling project in Hassi Messaoud and highlights the operational key factors and challenges faced during this particular and successful application in Algeria. Introduction The Hassi Messaoud field (Figure 2), discovered in 1956, is the largest oil field in Algeria, covering about 2000 Km2 and currently including over 1000 Wells. The field is divided aerially into 25 zones that are separated from each other by low permeability barriers, usually faults. The Cambrian Reservoir is subdivided into four lithological zones designated from base to top as R3, R2, Ra and Ri. The Ra sub reservoir shows the best petrophysical properties with a maximum thickness of 150 m in the western part of the field. The Ra is farther subdivided into five sub zones: D1, ID, D2, D3, and D4 based on reservoir properties and depositional conditions. This is the first of its kind Coiled Tubing - Underbalanced Drilling project undertaken in Hassi Messaoud field. The candidates wells are from a pool of vertical shut in wells drilled in the western area of the field and have seized to produce with varying completion string and production casing. The increase in number of candidates for thru tubing re-entries added to the depletion of the reservoir have raised the importance of use the combined technologies Coiled Tubing - Underbalanced drilling in Hassi Messaoud field. The original reservoir pressure was 6860 psi and the average permeability ranges from 0.5 to 1.0 mD but can reach up to 1000 mD in cases where open fractures are encountered. Production is 43.7 - 45 º API oil with original average GOR of about 200 m3/m3 and a formation temperature of approximately 120 ºC. Until 1964, the production mechanism was only depletion above bubble point. Gas injection and water injection started after that year to improve the production.
In Algeria about 60% of the proven oil reserves are in the Hassi Messaoud region which was discovered in the 1950's. Several oil production wells drilled over 40 years ago have been shut in and are awaiting workover plans to revive those wells and get them back into economic production. A typical workover program is comprised of extending the open-hole in the reservoir zone, below 7-inch casing, and producing that through a new 4-1/2-inch perforated production liner. At the time of initial drilling of those wells, the reservoir pressure was as high as that of the shale zone immediately above it. This reservoir pressure has now declined and can be found to be as low as one-third of the shale formation pressure. This recent variation in formation pressures (between exposed shale and reservoir zones) has created a need to mechanically isolate this exposed shale zone immediately above the lower pressure reservoir prior to drilling ahead. Original workover programs required the use of an additional (smaller size) casing string for this purpose, with the eventuality of drilling the reservoir open-hole section with a much smaller hole-size and completing the well as with a slim-hole configuration. This paper presents an alternative solution that was implemented to workover these type of wells and enable completion with a sufficient hole-size in the producing zone to avoid a slim-well configuration. The major technology used to facilitate this alternative workover was the installation of a solid expandable open-hole liner to mechanically isolate the high pressured shale zone above the reservoir. The aim was to still allow for a large enough open-hole passage in to the reservoir section to facilitate the use of high performance directional drilling BHA assemblies, The overall application of this workover is discussed to detail and highlight the added-value solid expandable liners provide in such workover applications. The successful integration and planning of the solid expandable installation along with; short radius casing exit, zonal isolation, and enhanced directional drilling has proven to be a significantly superior technical and economic alternative solution.
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