Central Asia has long been an area of interest for explorers, from ancient merchants to modern oil explorers. The region boasts some of the largest oil and gas fields in the world, including some major discoveries made within the last 20 years. In the 1960s significant investment in exploration was undertaken by the Union of Soviet Socialist Republics (USSR), which applied a rigorous exploration methodology across the region from extensive structural drilling to seismic and magnetotelluric acquisition. However, Soviet technology of the time had its limitations in computing power, seismic processing, acquisition and drilling technology. Following the fall of the USSR, many Western exploration companies have entered the Central Asian Republics in the hunt for hydrocarbons.
Central Asia lies in a fortunate location with energy-hungry markets such as Europe to the West and China, Pakistan and India to the East. Extensive pipeline infrastructure exists in many of the Central Asian republics with a range of new pipeline projects planned in the area. Tethys Petroleum is in the unique position of exploring three Central Asian Republics – Kazakhstan, Uzbekistan and Tajikistan – holding producing oil and gas fields and exploration acreage in the prolific Amu Darya, Ustyurt and Afghan-Tajik Basins.
Tethys has implemented modern, cutting-edge technology to explore and de-risk its exploration and maximize production. Here we present three case studies of the application of new seismic, magnetic and gravity and drilling technologies.
North Ustyurt Basin, Kazakhstan
In Kazakhstan, Tethys Petroleum maintains a strong presence in hydrocarbon exploration, development and production within the Akkulka and Kul-Bas licenses of the North Ustyurt Basin with proven reserves of 52.5 Bcfg and 5.8 MMbo and prospective resources of 634 Bcfg and 1230 MMbo respectively.
The North Ustyurt Basin lies immediately to the west of the Aral Sea and historical exploration within the area discovered shallow gas reservoirs of Eocene age. Initial exploration undertaken by Tethys Petroleum has furthered the understanding of these gas reservoirs with multiple discoveries, characterized by a seismic brightening on 2D seismic. In 2009–10, Tethys Petroleum drilled AKD01, the first well within the license area to flow oil at commercial rates from two deeper reservoirs of Upper Jurassic and Lower Cretaceous age. As part of the ongoing appraisal program associated with these discoveries, Tethys Petroleum acquired two 3D surveys across the area. Interpretation of the new data has included AVO analysis and color inversion techniques, and this information allowed further identification of multiple prospects for both shallow and deep reservoirs.
Following detailed mapping, it was apparent that alongside the structural traps associated with the Upper Jurassic reservoir, the Lower Cretaceous reservoir incorporates an important stratigraphic element. The analysis of attributes extracted from the seismic volume recognized the Lower Cretaceous reservoir as part of an established channel system. The extensive lateral coverage of this channel system, along with additional prospective fan systems, has proved encouraging for significant reservoir continuity and greater hydrocarbon potential as part of the ongoing exploration and appraisal program.
Afghan-Tajik Basin, Tajikistan
Tethys has been operating in Tajikistan for five years, holding a Production Sharing Contract (PSC) in the Afghan-Tajik Basin (34,785 km.), with unrisked prospective resources in excess of 113 Tcfg which were independently assessed in 2012. Current production in heavy and light oil occurs from Paleogene carbonate reservoirs (Beshtentyak, Kichikbel and Akbash Adyr oil fields) with some historic production from heavily fractured Cretaceous and Jurassic reservoirs (Komsomol field). Significant potential in Jurassic and Cretaceous intervals has been revealed by modern seismic, magnetic and gravity and drilling campaigns, although to date these intervals are largely unexplored.
Owing to the size of Tethys’ exploration acreage, a regional magnetics and gravity program was planned using ARKeX’s BlueQube Full Tensor Gravity and Magnetic acquisition, processing and interpretation services. The aim was to uncover the deep structure of the Afghan-Tajik Basin as well as to better delineate the sub-regional to local structure and its influence on prospectivity. The data was then used in conjunction with modern and vintage seismic datasets to plan a new seismic acquisition programme, which is currently underway.
The 2012 Tethys acquisition campaign is also utilizing new technology. The selected contractor Prospectiuni will be employing the SERCEL Unite, cable-free acquisition system, which will enable quicker and easier acquisition in the varied arable and mountain terrain of Tajikistan.
Amu Darya Basin, Uzbekistan
In 2009, Tethys Petroleum acquired the contractor rights to the North Urtabulak Production Enhancement Contract (PEC), whereby the contractor was obligated to implement new technologies and techniques to enhance liquid hydrocarbon production from the North Urtabulak oil field, which is reservoired in Jurassic reefal limestones.
Tethys Petroleum and its predecessors to the PEC, together with the state-owned oil company Uzbekneftegaz, had previously implemented horizontal drilling and sidetracking technologies as a means of accessing additional oil reserves. However, these capital-intensive and relatively high-risk technologies are no longer cost-effective for the North Urtabulak reservoir in its current state of depletion. Similarly, acid stimulation of the reservoir had been attempted at North Urtabulak, although it was found that the stimulation fluid tended to follow the path of least resistance, which is invariably into the lower productivity zones of the reservoir. It was therefore hoped that radial drilling might allow Tethys to more efficiently and accurately access trapped and/or previously inaccessible hydrocarbons.
Radial drilling’s principal application to date has been in marginal and mature fields with low productivity and shallow (<2,750m) wells. Radial drilling effectively applies modified coiled tubing technology to penetrate lateral holes of 50mm in diameter up to 100m from the original wellbore. The principal objective of this technique is to improve the production profile around the original wellbore by penetrating beyond the damaged skin zone and by accessing trapped pockets of hydrocarbons. At present this technology can only be applied in vertical (or near-vertical) wells, although research is ongoing to adapt this technique to deviated and horizontal wells. In total, five well candidates were selected for the radial drilling trial at North Urtabulak, with wells selected based on their production potential and mechanical condition. These were a combination of vertical and near vertical wells with cased-hole and open-hole completions located in different parts of the field. In four of the well candidates, one level of four laterals was attempted, and in well NU-116 two levels of four laterals were attempted. With the exception of well NU-44 (where only two laterals were achieved), in all the remaining wells four laterals of ~100m were successfully achieved at each level.
In conclusion, despite the pressure-depleted condition of the reservoir, the trial at North Urtabulak proved emphatically that radial drilling can be a cost-effective and time-efficient application to increase production and to access trapped hydrocarbons. It allows accurate placement of laterals and extended horizontal penetration over conventional perforating. It is a technology which Tethys Petroleum Limited fully intends to implement elsewhere, both in Uzbekistan and within the Tethys Petroleum Group’s other assets in Central Asia.
New Technologies the Future
The application of cutting-edge, cost-effective technology has opened up a wealth of new opportunity in Central Asia, from enhancing recovery in declining fields to exploring old basins with new technology. Tethys Petroleum and the countries that it operates in have benefited from the application of new technologies that have increased production and recovery and lowered exploration risk and cost.
The scope of opportunity and acreage on offer in Central Asia, and its position at the doorstep of numerous energy-hungry markets, makes the area an exciting place for exploration and development. With continued investment in exploration and infrastructure, the region has a very bright future.