Romashkino is the largest field in the Volga-Ural Basin, with a STOIIP of 38.8 BBO and EUR of 23.3 BBO. The main reservoirs are in the Devonian Pashiy and Kynov formations, which share an OWC across 4255 km². Since 1952, the 44 °API oil has been produced from lenticular and channelized tidal sandstones with average porosity and permeability of 19% and 375 mD, respectively.

Production built up steeply and plateaued at a phenomenal 1.7 MMBOPD from 1970-79. Ultimate recovery is on track for an equally impressive 60%. With ~25,000 wells littering the overlying countryside, it is tempting to attribute Romashkino’s success to the sheer number of wells. However, given the enormous productive area and thin oil column, the well count is hardly excessive. Benchmarking the reservoir against 431 suitable worldwide analogues shows that Romashkino has a well EUR that is slightly above the global average for its resource density.

A large success factor was the continuous optimization of the water injection strategy as new data became available. The field was divided into 21 development blocks corresponding to small structural highs. Injectors were placed parallel to the depth contours in the intervening lows but above the OWC (Fig. 1).

Initially, only the producers closest to the injectors responded to water injection. Updip producers either did not respond or continued to decline. Crestal injectors and additional rows of producers were added to improve the lateral sweep efficiency and maintain pressure (Fig. 2). However, vertical sweep was so poor that by 1965, only half of the flow units were being swept as water was lost to high-permeability layers.

Commingled injection was replaced by zonal injection, which improved the vertical production profile and enabled more effective injection at lower pressures. From 1968, the field was further subdivided into 406 sub-blocks – each with a tailored waterflooding strategy (Fig. 1).