The South Caspian Basin (SCB) covering a small area experienced intensive subsidence in the lower Pliocene and was isolated from the world ocean. The structures of the Baku Archipelago have one of the world’s most complex geological conditions for drilling, with rocks in the near well-bore area squeezed into the wellbore (the so-called well filling) when drilling through shales in the productive series, which account for as much as 90% of the Archipelago. Well filling leads to problems and accidents and triggers drilling mud blowouts and water/gas kicks, which often results in well abandonment.
The primary cause for well filling is abnormally high pore pressures in the cross-section of the structures, with gradients close to geostatic pressure gradients; such pressures are typical of thick shale strata. A study of shales found that shale porosity remained exceptionally high at great depths due to delays in shale compaction, the shortage of destressed zones and high rates of sediment subsidence.
Based on the core studies and measurements while drilling, various parameters were analyzed, including the density and porosity of shale samples taken in different years while drilling on the Baku Archipelago, in particular on the Umid structure. The compaction curve was plotted, and a potential zone of abnormally high pore pressures was delineated.

Keywords: South Caspian Basin, Baku Archipelago, productive series, shale deposits, abnormally high shale porosity, abnormally high pore pressure, shale compaction, drilling problems


REFERENCES

Aleksandrov B.L. Abnormally high reservoir pressures in oil and gas basins. Nedra. Moscow, 1987, 216 p. (in Russian).

Buryakovsky L.A., Dzhevanshir R.D., Aliyarov R.Yu. Geophysical methods of study of geofluidal pressures. Elm. Baku, 1986, 148 p. (in Russian).

Dobrynin V.M., Serebryakov V.A. Methods of prediction of abnormally high reservoir pressures. Nedra. Moscow, 1978, 232 p. (in Russian).

Efendiyev G., Isayev R., Piriverdiyev I. Decision-making while drilling wells based on the results of modeling the characteristics of rocks using probabilistic-statistical methods and fuzzy logic. ISAIC 2020, Journal of Physics: Conference Series, Vol. 1828, 2021, https://iopscience.iop.org/article/ 10.1088/1742-6596/1828/1/012016/pdf

Efendiyev G.M., Mammadov P.Z., Piriverdiyev I.A. Modeling and evaluation of rock properties based on integrated logging while drilling with the use of statistical methods and fuzzy logic. 10th International Conference on theory and application of soft computing, computing with words and perceptions – ICSCCW-2019. Advances in intelligent systems and computing book series (AISC), Vol. 1095, 2019, pp. 503-511.

Khalilov N.Yu., Balayev E.S. The effect of abnormally high reservoir pressures on reservoir and shale parameters in the Baku Archipelago areas. Gas Industry, Express Information, Series: Development of Oil and Gas Resources for Offshore Fields, Vol. 6, 1981, pp. 512 (in Russian).

Mekhtiyev P.G., Yusifov M.G. Specific features of distribution of abnormally high pore pressures in the Baku Archipelago areas. Oil and Gas Geology, No. 8, 1982, pp. 51-53 (in Russian).

Mkpese U.U. Estimation of overpressures from porosity based method: a theoretical approach applied to the central/coastal swamp depo-belts of the Niger delta basin. International Journal of Advanced Geosciences, Vol. 6, No. 1, 2018, pp. 14-26.

Shykhaliyev Yu.A., Feyzullayev A.A., Lerche I. Pre-drill over-pressure prediction in the South Caspian Basin using seismic data. Energy Exploration & Exploitation, Vol. 28, No. 5, 2010, pp. 397-410.