Technical and Technological Solutions for the Implementation of Hydraulic Fracturing in Conditions of Overpressured Reservoirs Beyond the Arctic Circle
Authors: Sayfutdinov Elnar , Suetin Sergey , Olender Oleg , Gaynetdinov Ruslan , Kazakov Evgeny 
Published: October 2019

As part of the implementation of unique projects of "Gazprom neft" in the regions located above the Arctic Circle, in difficult conditions of occurrence of Achimov deposits, it is necessary to apply new technical and technological approaches and solutions that are different from the standard conditions of hydraulic fracturing operations. The peculiarities of the mining and geological structure of the formations include the presence of abnormally high reservoir pressure with anomaly coefficient of 1.7 and high reservoir temperatures. One of the critical conditions is the autonomy of fields and climate conditions, which introduces additional challenges in the timing of the preparation and conducting of large-scale operations for hydraulic fracturing.

This article reviews the experience of the Company's specialists in preparing and implementing operations of the Company's first multi-stage hydraulic fracturing at Achimov facilities with abnormally high reservoir pressure during the winter period of 2019, provides technical features and limitations for well completion, features of selection and adjustment of hydraulic fracturing equipment and process fluids different from standard operations.

The features of the objects, which are under consideration, require more detailed and correct planning of each operation, starting from the completion stage, which includes features of the choice of the multi-stage HF arrangements, activation balls, sealing and locking devices. The article provides examples of calculating the required diameter of the balls to hold them in the saddle and prevent the "rollback" effect with high residual back pressure, especially the docking of the "stinger" in the tubing and liner suspension.

An important role is assigned to the integrated process of assessing and calculating potential risks within the framework of the cross-functional team. The method of "mastering on paper" is shown, in which the planning of each activity and stage is prescribed step by step, both within the Company and within the service organizations involved in the process (stocks of equipment capacity, spare parts, logistics, decision-making, etc.). The principle of drawing up and maintaining "road maps" as a method for monitoring and assessing the quality of current preparation and implementation of the process is also considered.

On the basis of conducted earlier single hydraulic fracturing on directional wells, the main "weaknesses" were identified, which were not previously taken into account when such projects were preparing and implementing. Conclusions based on this experience allowed more qualitative approach to the implementation of multi-stage HF, but did not take into account the changed features associated with the pumping of large volumes of proppant at 7-stage completion. Conducting the first operation of the multi-stage pilot operation showed that the standard approach is not enough. The time spent on the full cycle of hydraulic fracturing increased significantly compared with the planned and the field autonomy and climatic conditions made additional adjustments to adapt the technology to the new conditions.

Throughout the project, a cross-functional team of specialists was formed, whose work allowed us to quickly and efficiently respond to the emergence of both predictable and abnormal situations. He gained vast experience and strategy for making high-quality technical and technological decisions.

The result of the technical and technological improvements, including the well completion system, was the successful implementation of the program to stimulate the Achimov formations with the help of multiple fracturing mechanisms.

The experience and skills obtained allowed us to accelerate the development of wells with abnormal reservoir conditions and pressures. The vector of further optimization of the technological approach and technical solutions are given when performing a complex of works on the selection of completion and preparation of wells.

The assessment and a set of technical and technological solutions make it possible to implement and improve the hydraulic fracturing technologies on the Company's new Northern assets without additional complications and costs.