Hydraulic Fracturing Optimization Restores Development Prospectives in the Challenging Environment of Rostashinskoe Oilfield, Orenburg Region
Authors: Enikeev Ruslan , Nikulshin Evgeny , Picura Evgeny , Firsov Vladislav , Konchenko Andrey , Fedorov Andrey , Sukhanova Ksenia , Parkhonyuk Sergey , Klyubin Artem 
Published: September 2014

Orenburg region is a part of the Volga-Urals basin and it is represents the most difficulty for development and simulation. The Rostashinskoe is one of the fields of the Pervomaysky group and it is developing since 80th of the XX century. Main producing horizons of the field are Devonian age formations: Afoninsky (DV), Vorobievsky (DIV) and Ardatovsky (DIII) formations. Uniqueness of the Pervomaysky reservoir is very light oil with portion of light weight hydrocarbons (65-70%).

Oil traps of the Pervomaysky region Devonian formations are normally formed by one side faulting mechanism. Whole area of these oilfields is now covered by 3D seismic indicating traps relations to a series of regional faults scattered from east to the west. Apart from main regional faults Pervomaisky fields have quite a big number of smaller low-amplitude faults, both conductive and sealed. Presence of this faults significantly inputs into field development strategy. DIII formation of Rostashinskoe field is represented by two sandstone sub layers DIII-1 and DIII-2. Big number of faults and pinch out zones are establishing high degree of formation heterogeneity both vertically and laterally across the field. As a consequence of heterogeneity Rostashinskoe has a lot of difficulties with proper water flood and fracturing modelling in field development cycle. As a result, reserves are being recovered unequally across the field.

First trials of hydraulic fracturing on the oilfield starting from 2004 were unsuccessful with a huge number of difficulties such as: high fracturing treating pressure, large number of screen outs and finally difficulties with frac fluid flow back and well kick off up to full absence of inflow from the well. In order to investigate difficulties with flow back and fast production decline core analysis have been performed including mineralogical composition and core flow testing with fracturing fluid and it’s influence on core permeability. It was demonstrated that Rostashinskoe cores have problems with clay migration and wettability change. Based on performed core testing new clay stabilizer and surfactant has been suggested for fracturing fluid. Optimizations of fracturing fluid has led to significant improvement of final productivity results after fracturing and basically have proven efficiency of hydraulic fracturing for the Rostashinskoe field conditions. In 2010-2013 over 60 fracturing jobs performed on the Rostashinskoe oilfield. Corrections to candidate selection and frac design best practice has been made both taking into account well potential and current reserves recovery of DIII formation.

Success of the modified fracturing design has allowed to return the Rostashinskoe oilfield into active drilling program due to increased production, decreased production decline rate and finally better reserves recovery allowing to talk about "second live" of the Rostashinskoe oilfield.