Enhancing Recovery from the Oil-Rim Using Energy from the Gas Cap

In the environment of constant deterioration of resource base, stability of oil production in the nearest decades will depend on the prospects of development of geologically complicated fields. In Western Siberia significant part of undeveloped reserves is represented by highly viscous oil fields with gas cap. Such are Russkoye, Messoyakhskoye, Van-Yoganskoye, Severo-Komsomolskoye and other, having reserves over 4 bln. tons. Development of such assets is hindered by adverse geological and physical conditions. Presence of a gas cap and a fine oil rim leads to early gas breakthroughs. Viscous oil and poorly consolidated reservoir contribute to the risk of premature water breakthroughs (matrix breakthrough events), reducing the efficiency of injection. Permafrost and reservoir clay swelling limit the deployment of thermal techniques. The fields were discovered over 40 years ago and massive pilot work is being carried out only in Russkoye field, however, an efficient development technique has not yet been found. In such an environment it seems relevant to look into unconventional solutions. The authors propose an oil rim development technique using the energy of the gas cap. In this technique the design and the trajectory of horizontal wells allow for simultaneous controllable oil production from the oil saturated zone and gas production from the gas cap. This allows for enhancement of oil flow rate, reduction of gas coning and extends the period of stable well operation. The earlier achieved results of calculations made for Russkoye field have shown that while depletion recovery factor equals 6%, enhancement could provide up to extra 3%. In this work the authors, using modeling results, have determined optimal geo-technical conditions for deployment of this technique. Efficiency evaluation has been performed for operations at injection scheme. Particular features of this technique enable it to be viewed not only as an EOR technique, but also as a tool to prevent the main risks for similar fields, i.e. gas breakthroughs and reservoir damage. Based on the results of the study proposals were elaborated for pilot work in Russkoye field.