Successful Restimulation of Western Siberian Oil Fields with Channel Fracturing Technique
Authors: Yudin Alexey , Rapeyko Vitaliy , Kuznetsov Maxim A. , Pritula Igor I. , Ibragimov Kenes R , Gorbunov Dmitry , Rudnitsky Andrey Alexandrovich 
Published: March 2015

Western Siberia's Jurassic and Achimov formations are well known for low permeability, high heterogeneity, and lamination in which the majority of the wells require stimulation. However, production declines call for restimulation operations to improve field economics. Common challenges for both fracturing and refracturing treatments include achieving considerable effective half-length and increasing fracture conductivity while reducing screenout rates, which average 10%. To solve both problems, the channel fracturing technique was implemented.

The channel fracturing technique changes the concept of proppant fracture conductivity generation by enabling hydrocarbons to flow through open channels instead of the proppant pack. The new technique is based on four main components: proppant pulsing at surface with fracturing equipment and software, a special perforation strategy, fibrous material to deliver stable channels, and a set of models to optimize channels geometry.

The use of the channel fracturing technique enabled economical production from 10 restimulated wells. Also, a reduction in screen outs was seen during refracturing treatments, which was an important advantage of the new method over the conventional stimulation technique based on homogeneous proppant placement.

Bottomhole pressure gauges were used consistently throughout the campaign to study friction pressure and net pressure behavior during channel fracturing jobs. Overall, zero screen outs occurred throughout the campaign and well productivity was 15% to 30% higher when restimulated with channel fracturing.

Introduction

Reduction in drilling of new wells and overall production decline forces an operator to look for the ways to produce economically from old wells in developed areas. Refracturing of previously stimulated wells is a remedial technique to increase production rate and recover incremental reserves. Restimulation treatments bypass near-wellbore damage, re-establish good connectivity with the reservoir and tap areas with higher pore pressure. At the same time refracturing often requires pumping more proppant and more aggressive design than at first treatment increasing risk of premature screenout. In addition poor workover operations, depleted reservoir pressure and current negative skin may result in low or even negative production effect. In these conditions operator needs an innovative refracturing technique that can provide economically viable long-term performance. The channel fracturing concept applied in Taylakovskoe and Vatinskoe fields proved to be effective in such difficult environment.

Refracturing overview

First candidates for refracturing are usually wells with inadequate initial treatments, with operational problems during placement, etc. In this case the only question for refracturing treatment is to identify the occurred during first attempt problem and fix it by successful second attempt, how to perform the job must be considered in each particular case.

Completely different situation when initial fracture performed as per schedule, what can be the benefit of performing refracturing for this well? Two scenarios can be considered in this case:Predicted production after initial treatment was not achieved.

On the one hand oil is still there, well might still have a potential, but on the other hand one should be carefully planning refracturing for such well, as it was shown by Parrot et al., 1979 and Reese et al., 1994: poor well cannot be made any better with a refracturing job. In particular formation pressure, permeability and offset wells performance should be investigated.