Abstract

Chemical treatments of water injectors have been performed at the Romashkino oil field located in Tatarstan (Russia). This sandstone reservoir is heterogeneous (9 to 12 layers) and fractures are suspected due to its extensive water-flooding for decades. Since 1992, 134 injection wells have been treated for conformance control with 12,000 to 20,000 bbl of hydroxylethyl-cellulose suspensions. The additional oil obtained from the 494 offset producers amounts 4.6 millions barrels and corresponds to 6,500 bopd.

Production data are presented for a selected zone: 12 injectors and 35 producers. It is shown that the treatments have resulted in the areal and vertical modifications of the sweeping efficiency of water.

Introduction

The number of field tests using polymer/gels to prevent excessive water production has considerably risen since the beginning of the '90s.1–7 The application of the technology based on the thermal formation of gels from polyacrylamides and metal or organic chelates has gained considerable interests and increasing numbers of successes are reported in the oil and gas industry. This technology has brought obvious technical improvements and although it is becoming prominent, no water control technique is ubiquitous and numerous other systems are applied.

Better evaluation of the possible treatments, tighter screening criteria and improved chemical systems are responsible of the recent higher rate of successes, but great care in the design is still required.8,9 Although correct identification of the water problem is one of the key parameter for success, this is rarely obtained both for practical or economical reasons. Strong interests in treatments without zone-isolation do exist, and developments of selective systems aiming to mechanical selective placement10 or to water/hydrocarbon relative permeabilities selective modifications are underway.

In heterogeneous reservoirs, the main factors leading to water channeling in natural water drive and water flooded reservoirs are the presence of fractures and high permeability streaks. Undesirable influx of water into thief zones causes premature breakthrough of water, leaving unswept oil in lower permeability zones.

The Romashkino giant oil field located in Tatarstan (Russia) discovered in 1948 has been exploited since 1952 by waterflooding. Since 1992, the Tataril national oil company TATNEFT and TOTAL have created the TATOLPETRO company to perform polymer profile modification treatments of water injectors in order to produce additional oil. The type of polymer used in this process is a high quality grade of hydroxyl-ethyl-cellulose (HEC). By the beginning of 1996, 134 injectors have been treated and 494 offset producers have led to a daily additional oil production of 6,500 bpd.

After a brief overview of the different water shutoff chemical technologies, this paper with present detailed field results of a selected zone.

Review of Water-Control Chemical Technology

Water shutoff covers a broad range of techniques and can refer to organic or inorganic polymer/gels, cements, resins, foams, particulates, emulsions, micro-organisms, precipitates, mechanical devices (packers, bridge-plus, . . .), infill drilling, pattern flow control and horizontal wells.

For chemical technologies, difference between near well bore or in depth profile modification treatments and reservoir mobility control process (such as polymer flood) nneeds to be first outlined. In mobility control techniques, the polymer needs to penetrate as far as possible into the low permeable oil bearing zone to ensure the efficiency of the oil displacement due to increased viscosity of the mobile agent. But for profile modification treatments, polymer/gel should enter as less as possible the oil productive zones, in order not to reduce or annihilate any wanted oil production due to influx modification of the displacing agent (water or gas).

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