Summary
The largest discovery of oil and gas in recent years is situated in the Volga-Ural field in Orenburg Oblast. The field was discovered in 2005. The development target is the Devonian Dkt formation which is an aggregate of ancient strata in the Earth's crust that were formed during the Devonian Period of the Paleozoic Era. The Devonian System is divided into a Lower, Middle and Upper series. It consists of alternating layers of sandstone-claystones and siltstones, which have low permeability. Hydraulic fracturing is required to obtain hydrocarbon inflow from this type of rock.
The well design employed in the Volga-Ural field incorporates five casing strings and the main challenge while drilling wells in this field is lost circulation. This ranges from partial fluid loss to no returns and has a significant impact on the cementation of the 178/146 mm production casing. Lost circulation has resulted in a failure to achieve the targeted top of cement, annular pressure, annular crossflows and a poor cement bond with both the casing and formation. Prior to 2015, a stage cementing collar (SCC) technique was used to cement the production casing without losses. However, this cementing technique often resulted in poor zonal isolation resulting in water flows between zones. Additionally, after well completion, poor cement bonding to both the casing string and producing formation created a pathway for annular flow of the formation fluids. These challenges called for an alternate solution. This paper presents how foamed cementing technology was used to solve the challenges in isolation of the sandstones and the subsequent improvement of the cementing bond quality. The foam cementing technique was tested in the Volga-Ural field at the end of 2015 and in early 2016 and became the standard solution for cementing the 178/146 mm production.
