Abstract

Matrix acidizing of sandstone formations in Western Siberia, Russia has been a technology application that has been largely ignored by operators in this area. Poor acidizing practices and difficult mineralogies have lead to poor results from matrix acidizing treatments applied in the past. With the relative success of skin bypass fracturing treatments and the development of a fracturing stimulation environment within Russia, matrix acidizing has been rendered essentially irrelevant. This paper reviews past and present practices and explores the reasons why matrix stimulation has been largely unsuccessful in Western Siberia. The paper also explores the developing need for matrix treatments, particularly in horizontal wells, and the application of modern acidizing systems and techniques in Western Siberia and the challenges associated with applying these "new" technologies

Introduction

Russia's Siberian basins are extensive in area, and vary greatly in their geology and the degree to which they have been explored and exploited (Figure 1). The fields in Western Siberian produce from Jurassic and Cretaceous reservoirs and are sourced from the same intervals. The West Siberian Basin contains over 645 oil and gas fields and produces approximately 80% of all Russia's oil and gas.The fields of the East Siberian Platform have different petroleum systems that locally include source and reservoir rock from the late Precambrian era. This Eastern area is largely unexplored and undeveloped[1].

The Western Siberia basin is one of the largest in the world, extending from the Eastern Urals to the Yenisei River and from the Arctic Ocean to the Kazakh uplands. This is approximately 2.1 million km2 in area and does not include offshore areas of the same structures under southern Kara Sea. The basin can be described broadly as a "young", three layered structure consisting of a heterogeneous basement, an intermediate pre-platform complex of Paleozoic-Triassic volcano - sedimentary rocks and a platform of Meso-Cenozoic deposits that are predominantly Jurassic and Cretaceous. The area has been strongly influenced by a branched rift system that determined the sedimentary deposition patterns and structural features of the later oil and gas bearing rocks of the Jurassic and Cretaceous.

Systematic exploration of the area started in 1948 with the first gas field (Berezovskoye) discovered in 1953 and followed by the first oil field (Shaimskoye) discovery in 1960. In the next decade, exploration advanced to the central and northern areas of Western Siberia, where the giant-large oil and gas fields of Samotlor, Urengoi, Medvezhiye Yamburg and others were discovered.

Most of these fields are associated with the Cretaceous and Jurassic deposits that are the major production targets. Comparatively small fields have been found in Paleozoic deposits with minor oil and gas shows associated with Triassic rocks. Most reservoirs are of anticlinal type, uplifted layered or massive, sometimes stratigraphic and lithological. The sedimentary cover contains two homogeneous argillaceous regional caps: the Upper Jurassic (Valanginian) and the Paleogene (Turonian). These caps seal the two main oil-and-gas complexes of the Jurassic and Cretaceous age respectively.

Most oil fields of the West Siberia are associated with the central and to a lesser degree southern areas of the province. The northern areas are characterized either by gas fields, gas-prevalent or gas and gas condensate fields.

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