TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractChina National Offshore Oil Corporation (CNOOC), Chevron, and ENI, the field operator, are partners in the development of the HZ oil and gas fields, operating as the CACT Operators Group (CACT) in the South China Sea. The HZ fields are stacked, thin, high-permeability sandstone reservoirs interlayered with low-permeability layers. The shallower layers generally have better permeability and were developed first while the deeper, lower-permeability reservoirs have been developed more recently.The lower-permeability reservoirs are generally of lower porosity and higher compressive strength. Drilling-mudfiltrate invasion also tends to be deeper. Deep-penetration perforating charges are required to perforate past the damaged zone. Experience indicates that underbalance perforation provides better productivity compared to overbalance perforation.Although conventional underbalance perforation can be performed using pipe-conveyed or tubing-conveyed perforation (TCP), depth uncertainties and the time requirement for TCP service in thin reservoir zones makes wireline-conveyed perforation an attractive method. However, where multiple zones must be perforated, the conventional wireline approach can only perforate the first zone underbalance (with the completion fluid weighted accordingly) while subsequent zones could only be perforated balanced at best. A new perforating system, designed to generate a large dynamic underbalance with a static overbalance, was used to perforate new wells for the development project to maximize well productivity per well expenditure.A multilayer production evaluation of one of the wells perforated with the dynamic underbalance method produced a zero skin value in the 9-md layer and a -0.97 skin value in the 1600-md layer. Conventional underbalanced perforation, employing multiple wireline runs, could not achieve these low skin values over this wide range of permeabilities. and z w = 15.4 ft in TVD, θ= 32 deg) 1.672 +/− 0.5 Completion Skin Factor Sensitivity Analysis Completion Skin Factor = 2 J ss , PI (STB/D/psi) 12.449 2.600 (stdev) J pss , PI (STB/D/psi) 13.254 2.780 (stdev) Completion Skin Factor = 1 J ss , PI (STB/D/psi) 13.546 2.931 (stdev) J pss , PI (STB/D/psi) 14.504 3.153 (stdev) Completion Skin Factor = 0 J ss , PI (STB/D/psi) 14.854 3.261 (stdev) J pss , PI (STB/D/psi) 16.015 3.537 (stdev) Completion Skin Factor = −1 J ss , PI (STB/D/psi) 16.443 3.607 (stdev) J pss , PI (STB/D/psi) 17.876 3.953 (stdev) Completion Skin Factor = −2 J ss , PI (STB/D/psi) 18.412 3.934 (stdev) J pss , PI (STB/D/psi) 20.228 4.377 (stdev)
VICO Indonesia is the operator of the Sanga-Sanga Production Sharing Contract located onshore of the Mahakam delta, East Kalimantan, Indonesia since 1968. Over 40 years the PSC has produced 70% of the estimated original gas in place, supporting Bontang LNG plant. VICO has 7 producing fields, in a complex fluvial deltaic deposition with more than 2700 gas and oil reservoir, mixed of depletion and water drive mechanism reservoir. VICO production peaked at 1.5 BSCFD in 1995 then start to decline. Current production is in the range 385 MMSCFD of gas and 14500 BOPD of liquids from 400 active wells. In a situation of 46% annual base decline, to fulfill domestic and LNG contractual commitments and to optimize reserve recovery, VICO generated and implemented an integrated and aggressive work program called "Renewal Plan". This is an integrated approach between reservoir management and technology application; it provides a detail road map to onward development strategy. The main elements of the plan are extensive development drilling activities (conventional drilling, grid base drilling, cluster well drilling), low permeability reservoir optimization (horizontal well, hydraulic fracturing, radial drilling), production optimization (deliquification technique, permanent coil tubing gas lift for monobore type) and facilities optimization (reducing abandonment pressure by additional compression installation, wellhead compressor, debottlenecking). Technology application in drilling, completions, production and facilities optimization combine with synergy from multidisciplinary team have resulted in maintaining VICO production decline in the range of 5% (vs 46% base decline), allowing promoting and partially replacing the reserves at an attractive development cost, even after 40 years production life. This paper will describe the successful implementation of renewal plan in VICO Indonesia, which proved to be an efficient example of better reservoir management for optimum development of mature assets.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractChina National Offshore Oil Corporation (CNOOC), Chevron, and ENI, the field operator, are partners in the development of the HZ oil and gas fields, operating as the CACT Operators Group (CACT) in the South China Sea. The HZ fields are stacked, thin, high-permeability sandstone reservoirs interlayered with low-permeability layers. The shallower layers generally have better permeability and were developed first while the deeper, lower-permeability reservoirs have been developed more recently.The lower-permeability reservoirs are generally of lower porosity and higher compressive strength. Drilling-mudfiltrate invasion also tends to be deeper. Deep-penetration perforating charges are required to perforate past the damaged zone. Experience indicates that underbalance perforation provides better productivity compared to overbalance perforation.Although conventional underbalance perforation can be performed using pipe-conveyed or tubing-conveyed perforation (TCP), depth uncertainties and the time requirement for TCP service in thin reservoir zones makes wireline-conveyed perforation an attractive method. However, where multiple zones must be perforated, the conventional wireline approach can only perforate the first zone underbalance (with the completion fluid weighted accordingly) while subsequent zones could only be perforated balanced at best. A new perforating system, designed to generate a large dynamic underbalance with a static overbalance, was used to perforate new wells for the development project to maximize well productivity per well expenditure.A multilayer production evaluation of one of the wells perforated with the dynamic underbalance method produced a zero skin value in the 9-md layer and a -0.97 skin value in the 1600-md layer. Conventional underbalanced perforation, employing multiple wireline runs, could not achieve these low skin values over this wide range of permeabilities. and z w = 15.4 ft in TVD, θ= 32 deg) 1.672 +/− 0.5 Completion Skin Factor Sensitivity Analysis Completion Skin Factor = 2 J ss , PI (STB/D/psi) 12.449 2.600 (stdev) J pss , PI (STB/D/psi) 13.254 2.780 (stdev) Completion Skin Factor = 1 J ss , PI (STB/D/psi) 13.546 2.931 (stdev) J pss , PI (STB/D/psi) 14.504 3.153 (stdev) Completion Skin Factor = 0 J ss , PI (STB/D/psi) 14.854 3.261 (stdev) J pss , PI (STB/D/psi) 16.015 3.537 (stdev) Completion Skin Factor = −1 J ss , PI (STB/D/psi) 16.443 3.607 (stdev) J pss , PI (STB/D/psi) 17.876 3.953 (stdev) Completion Skin Factor = −2 J ss , PI (STB/D/psi) 18.412 3.934 (stdev) J pss , PI (STB/D/psi) 20.228 4.377 (stdev)
VICO Indonesia is the operator of the Sanga-Sanga Production Sharing Contract; located onshore of the Mahakam delta, in East Kalimantan, Indonesia. Since inception the PSC has produced over 70% of the estimated original gas in place. The fields are relatively mature with most of the remaining gas resources locked up within the lower permeability reservoirs, where conventional tight-gas completion approaches have not been very effective in ensuring depletion of the resource. A valuable prize of at least 0.5 TCF would be readily achievable, if these lower permeability resources could successfully be developed and recovered. The lower permeability formations being referred to; are typically sub milli-darcy, and the ability to achieve any kind of sustainable economic production rate has been extremely problematic. Previous attempts at hydraulic fracturing within VICO, over nearly three decades, have been dramatically ineffective and have rarely enjoyed any sustained production improvement at all. Geologically the reservoirs are best described as distributary river channels, in a lower deltaic plain environment and therefore these individual sands can vary in size and connectivity quite substantially. Alternative technologies, such as horizontal drilling are being applied, but only within those sand bodies which are larger and which can therefore readily support the economics associated with horizontal well drilling. In 2006 a detailed technical review of the previous 30 Years of hydraulic fracturing operations was commissioned, this review noted that there were five basic ‘skins’, which were causing problems for hydraulic fracturing. These ‘skins’ were: wellbore integrity, execution QA/QC, relative-permeability, regional tectonics and poro-elasticity. The data was extremely convincing and based upon the review a decision was made to implement a five well pilot in order to confirm the findings and present solutions. This paper will describe the long and difficult journey of VICO hydraulic fracturing, from the original treatments through the recent review, the fracturing pilot from 2007 - 2009 and into the early stages of the new fracturing campaign planned for 2010 - 2012, The paper will present the results of the detailed study, the implementation phase of the pilot and the forward plan for the VICO low permeability zone(s) based upon the significant progress, successes and deliverables of the fracturing pilot in the Nilam G-Sands.
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