Kazakhstan journal for oil & gas industry

2707-42262957-806X

KMG Engineering

108969

10.54859/kjogi108969

Comprehensive Interpretation of Geochemical, Physicochemical Studies and PVT Parameters for Verification of Phase Zonation of Reservoirs (A Case Study of the Vostochny Urikhtau Field)

Jarassova

Tolganay

PhD, Senior Researcher at the Department of Core Researcht.jarassova@kmge.kzhttps://orcid.org/0000-0002-2900-9872Seitkhaziyev

Y. Sh.

Y.Seitkhaziyev@kmge.kzhttps://orcid.org/0000-0001-5655-3112Aldebek

Almira Ye.

a.aldebek@kmge.kzhttps://orcid.org/0009-0004-2233-4412Ykhlassov

Nauryzbay

N.Ykhlassov@kmge.kzhttps://orcid.org/0009-0006-5911-918X

Atyrau branch of LLP "KMG Engineering"Atyrau Branch of KMG ENGINEERING LLPAtyrau branch of KMG Engineering82

31032026

22052026

Background. Correct identification of the fluid phase state (oil or gas condensate) at the Vostochny Urikhtau field is critical for reliable reserve estimation and development strategy selection. Anomalous gas-oil ratio values in wells VU-6 and VU-7 (up to 1000 m³/m³) and discrepancies in the hypsometric levels of the presumed gas-oil contact with regional data create uncertainty that requires resolution through an integrated approach. Aim. To determine the genetic and phase affiliation of reservoir hydrocarbon systems at the Vostochny Urikhtau field across seven wells using a multidisciplinary approach. Materials and Methods. The study objects were seven deep fluid samples from wells VU-1 to VU-8. The analytical program included gas chromatography (GC), gas chromatography–mass spectrometry (GC-MS), fingerprinting, biomarker analysis (steranes, terpanes, aromatic hydrocarbons), as well as physicochemical and PVT studies using a FLUIDEVAL system with visual phase behavior monitoring. Results. Biomarker analysis confirmed the genetic uniformity of all samples: the fluids originated from a single marine carbonate source rock. Based on a set of criteria (density 780 kg/m³, molecular weight 150 g/mol, C7+ content 85%, Σ(C1–C9)/Σ(C10+) ratio 1), all samples were classified as oil. The sample from well VU-7 was identified as volatile oil. PVT studies and visual observations ruled out the presence of gas condensate systems. The established phase model corresponds to an oil reservoir with gravitational segregation and a volatile oil transition zone in the crestal part, without a conventional gas cap. Conclusion. The applied multidisciplinary approach allowed verification of the fluid phase zonation at Vostochny Urikhtau. The substantiated reservoir model (oil rim without a separate gas cap) necessitates the use of the volumetric method for reserve estimation and consideration of the identified phase heterogeneity in development system design to minimize geological risks and ensure accurate resource assessment.

fluid phase zonation, biomarker analysis, gas-oil ratio (GOR), PVT, Vostochny Urikhtau, Caspian Basin

флюидтердің фазалық аймақтылығы, биомаркерлік талдау, газ факторы, PVT, Шығыс Өріхтау, Каспий маңы ойпаты

фазовая зональность флюидов, биомаркерный анализ, газовый фактор (ГФ), PVT, Восточный Урихтау, Прикаспийская впадина

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