Revealing New Exploration Plays in the Deeper Parts of the Ustyurt Region in Uzbekistan
Authors: Yessalina S. A. , Gulamov R. A. , Mallaev S. E. , Muratov A. S. , Muminov M. N. , Kuvanyshev A. M. , Khairaliyev B. S. , Shaikhina D. S. , Byashimova T. S. , Yensepbayev G. T. , Ashimov Z. Y. 
Published: May 2024

Abstract

Objectives/Scope
The Berdakh-Sudochi region, the promising frontier exploration area of Uzbekistan have been studied for basin modeling to optimize exploration drilling campaign. The objective of this study was to assess the overall potential of deeper poorly explored Lower Jurassic sequences, based on analyses of field data, regional geological framework and petroleum system.

Methods, Procedures, Process
An integrated approach has been applied for petroleum system modeling of the Jurassic sediments in the study area. The basin models have been built based on comprehensive review of all collected regional geological, geophysical, and field data. Interpreted seismic data have been utilized to build the subsurface structural framework of the basin. Distribution of depositional facies have been constrained based on analyses of well logs, seismic attributes, core data and existing regional studies. This basic geological concept served as the main input for assessment of petroleum system elements and reconstruction of burial and thermal histories.

Results, Observations, Conclusions
The Jurassic formations in the study area were controlled by the development of the Sudochi paleorift active till Lower Jurassic. Active rifting had dramatic effects on hydrocarbon system. The paleorift provided an effective kitchen for organic maturation in the deeper subsided part of the region. Rapid sedimentation led to deposition of thick basal reservoir rocks at the margins of the basin. The results of regional geological studies and petroleum system modeling showed promising potential for the Lower Jurassic sediments underlying the producing intervals. Reconstructed burial and thermal histories favor the Lower Jurassic in terms of hydrocarbon generation and timing of expulsion. High subsidence rates created favorable conditions for preservation and maturation of distal Lower Jurassic organic-rich sediments, with gas window starting at depth range of 3-4 km. The proximal Lower Jurassic fan deposits represent the best reservoir in terms of net thickness and continuity, overlain by fining upward fluvial sediments of Middle and Upper Jurassic. Close vicinity between kitchen and reservoir rocks facilitated effective migration and charge of traps. Recommended deepening of the existing wells till depth of 4500 m targeting Lower Jurassic fans has proved high potential of the sequence with commercial flow rates up to 1 MMscm/d. The new deep wells were planned at different parts of the paleo-rift to develop the new play. After drilling success followed by increase in production drilling an appraisal well down to 6500m was proposed and approved to explore the deeper syn-rift deposits and traps.

Novel/Additive Information
This work represents multidisciplinary study integrating regional geological and geophysical data. highlighting importance of petroleum system studies in reducing exploration risks by defining most promising targets for drilling. The results of this work opened new opportunities and had crucial impact on governmental decision to boost exploration activity in the Ustyurt region.