Qo‘sbuloq botig‘ining shimoliy va janubi-g‘arbiy qanotlaridagi yura yotqiziqlarining neft-gaz hosil qiluvchi salohiyati (Shimoliy Ustyurt havzasi, Qozog‘iston): ikki qidiruv qudug‘ida Rock-Eval piroliz ma’lumotlari

Annotatsiya

The Kosbulak Trough, in the eastern part of the North Ustyurt Basin in western Kazakhstan near the border with Uzbekistan, is one of the deepest Mesozoic depocentres of the basin, yet published organic geochemical data on its source rocks remain scarce. This study evaluates Rock-Eval pyrolysis data from two exploration wells located on opposite flanks of the trough: Well N on the northern flank (11 cuttings samples, 1657–1975 m depth) and Well S on the south-western flank (752 cuttings samples, 450–4688 m depth). Formation tops from well logs and palynology were used to compare the same stratigraphic units in both wells. In Well N, the Middle Jurassic coal-bearing interval (1685–1875 m depth) has median TOC of 5.81 wt.% (up to 32.2 wt.% in coal), S2 of 1.08–31.59 mg HC/g rock and HI of 43–189 mg HC/g TOC, indicating gas-prone Type III organic matter; Tmax of 424–429 °C and measured vitrinite reflectance of 0.43–0.44% show that it is thermally immature. In Well S, the Middle Jurassic (3242–4010 m depth) is leaner (median TOC 1.06 wt.%, median S2 1.16 mg HC/g rock), but its richest coaly beds at 3522–3563 m depth (TOC 3.32–4.93 wt.%, S2 5.41–8.34 mg HC/g rock) have Tmax of 435–441 °C, corresponding to the onset of the oil window. In the Lower Jurassic and Triassic of Well S (below 4010 m depth), Tmax decreases to about 407 °C; this is attributed to low S2, oil-based-mud contamination and bitumen impregnation observed in core, rather than to decreasing maturity. Regional vitrinite reflectance and palaeotemperature data support this interpretation. The results indicate that Middle Jurassic source rocks are richer but immature on the northern flank and leaner but more mature on the deeper south-western flank; the deeper axial part of the trough, not sampled here, is suggested as the most probable gas-prone generation area.

Inglizcha annotatsiya noshirning maqola sahifasidan olingan. Mualliflar annotatsiyasi CC BY 4.0 litsenziyasi asosida keltirilgan. Annotatsiya ingliz tilida berilgan.

Kalit so‘zlar

• Shimoliy Ustyurt havzasi
• Qo‘sbuloq botig‘i
• yura
• geotermik gradient
• qatlam harorati
• Rock-Eval pirolizi
• cho‘kish tarixi

Sodda qilib aytganda

Qo‘sbuloq botig‘i Qozog‘istonning g‘arbi va O‘zbekiston hududidagi Shimoliy Ustyurt havzasining sharqiy qismida, O‘zbekiston chegarasi yaqinida joylashgan. Yura asosi uning shimoliy qanotida taxminan 1,8–2,2 km dan janubi-g‘arbiy qanotida 4,2–4,4 km gacha, botiq o‘qida esa 4,6 km gacha chuqurlashadi. Poydevor taxminan 11–12 km chuqurlikda yotadi; yura davridan beri botiq sezilarli ko‘tarilish va yemirilishsiz uzluksiz cho‘kib kelgan.

Mualliflar bir-biridan taxminan 80 km uzoqlikdagi ikki qidiruv qudug‘i shlamini tahlil qilgan: shimoliy qanotdagi N qudug‘idan 11 ta namuna (1 657–1 975 m) va janubi-g‘arbiy qanotdagi S qudug‘idan 752 ta namuna (450–4 688 m); qatlam chegaralari karotaj va palinologiya bo‘yicha aniqlangan. N qudug‘ida ko‘mirli o‘rta yura (1 685–1 875 m) organik moddaga boy, ammo termik jihatdan yetilmagan (Tmax 424–429 °C, vitrinitning aks ettirish qobiliyati 0,43–0,44%). S qudug‘ida o‘rta yura (3 242–4 010 m) kambag‘alroq, biroq 3 522–3 563 m chuqurlikdagi eng boy ko‘mirli qatlamlarida Tmax 435–441 °C ga yetadi — bu neft oynasining boshlanishi. Ikkala quduqda ham organik modda asosan gaz hosil qiluvchi, III turga mansub.

Ikkala quduqning cho‘kish tarixi yura davridan beri uzluksiz cho‘kishni ko‘rsatadi (7-rasm). Mintaqaviy hozirgi geotermik gradient (30–36,6 °C/km) asosida mualliflar o‘rta yuraning hozirgi haroratini N qudug‘ida taxminan 70–75 °C, S qudug‘ida esa 120–160 °C deb baholaydi. Mintaqaviy ma’lumotlarga ko‘ra, botiqning janubi-g‘arbida 3 700–4 100 m chuqurlikda hozirgi qatlam harorati 155–175 °C, undan shimoli-g‘arbda 2 300–2 400 m chuqurlikda 72 °C; o‘rta yura asosidagi paleoharoratlar 160–175 °C dan taxminan 190 °C gacha. Mualliflar gaz hosil bo‘lishining eng ehtimolli hududi deb botiqning o‘rganilmagan o‘q qismini ko‘rsatadi.

Rasmlar (1)

Iqtibos namunasi

Zhanna Bekeshova, Kosarbay Kozhakhmet and Nurlygul Kylyshbayeva (2026). Source-Rock Potential of Jurassic Deposits on the Northern and South-Western Flanks of the Kosbulak Trough (North Ustyurt Basin, Kazakhstan): Evidence from Rock-Eval Pyrolysis of Two Exploration Wells. Energies, vol. 19, no. 21, 5097. https://doi.org/10.3390/en19215097