Caspian Experience Boosts Performance in Turkey’s Onshore UGS Project
Authors: Carpenter Chris 
Published: October 2023

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 207011, “Healthy Caspian Experience Helps Boost Drilling Performance in Turkey’s Onshore UGS Project,” by Elchin Akbarli and Rufat Mammadbayli, SPE, SOCAR AQS. The paper has not been peer reviewed.

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In the complete paper, the authors describe an operator’s underground gas storage (UGS) project. The intent of the paper is to demonstrate the execution methodology and technologies that the company used to deliver the work on time and under budget. The authors outline planning, design, and drilling and completion strategies used during the execution phase. The authors add that the company’s experience in Caspian operations was of great benefit to the project.

Introduction

A plan was developed to expand a UGS facility in a salt cavern field. The main challenge of the project was the requirement to complete all wells within a short time frame with a limited budget while keeping the project economically feasible for the company without compromising safety and environmental protection.

Geological risks and uncertainties required additional preliminary considerations, leading to a focus on the best methods available for the drilling and completion of 40 planned wells. A comprehensive cost analysis was performed to evaluate the approach. The operations were divided into three stages: tophole drilling, main drilling, and completion. Different types of rigs, with different capabilities depending upon the range of the work, were assigned for each phase. The plan involved three small truck-mounted mobile rigs to begin tophole drilling and run 30-in. conductor casings to isolate unconsolidated formations and freshwater zones. Then, six main rigs would be mobilized to perform the main stages of drilling; three completion rigs would finalize the project.

The company’s Caspian experience applied to several technical aspects of the project, from optimization of drilling activities to planning and execution. The project presented many technical challenges, including geological hazards, deviation control, and strict requirements of well integrity for a long period of time.

Rig Specifications for Drilling Stages

A major decision point in the planning phase was to select different types of rigs to implement various drilling operations in a staged manner. Initially, 125-ton-capacity truck-mounted rigs began to drill 36-in. tophole sections and run 30-in. casings; then, the task was passed to main drilling rigs with installed 30-in. conductor casing. Top holes were drilled with three low-cost, low-capacity rigs to combat the high potential of lost-circulation problems that could be experienced with high-cost main drilling rigs. In the second stage, main drilling rigs with 225-ton and 300-ton capacity were involved for the next 26- and 17½-in. sections. In the third stage, low-capacity rigs were moved to the well locations to complete wells, either running the last leaching string of 10- and 7-in. casings or underreaming 12-in. to 17½-in. sections before running leaching strings.