| Block Wa38 is structurally situated at the northward of southern descent belt with central uplift in Liaohe fault. Sha3 layer is in the major layer series of development in this block covering the explored oil bearing area of 3.1km~2, and 962×10~4t for OIIP. The buried depth of the reservoir is-1290～-1490 m. The density of the crude oil is 0.987g/cm~3 at 20℃, and the viscosity of the stock tank oil is 12600mPa.s at 50℃. The reservoir is an extra heavy oil reservoir with tremendous thick layer. In 1990, it was developed with huff & puff by adopting 100m square well pattern (and in part with 70m well spaces). By the end of December of 2004, there had been 98 brought-in wells in totals and 60 wells startup. The average daily oil production for single well was 2.2t/d, and annual oil production was 3.98×10~4t, followed by 231×10~4t for cumulative oil production, 347×10~4m~3 for cumulative water production, 0.67 for cumulative ratio of oil to steam, 87.04% for composite water cut, and 99.3% for water back production. The average cycle for single well was 9, the oil production rate was 0.42%, and the degree of reserve recovery reached 24%, and 98% of the recoverable reserves had been achieved with steam drive treatment.At present, the block is in the last stage of steam stimulation. The existing problems now include that the formation pressure has decreased to 15% of the original formation pressure, the oil production and ratio of oil to steam are constantly declined, and the ratio of oil to steam for steam stimulation is approximately to the ratio of economic limit. Since the development potential is limited as continuing developed by huff and puff for heavy oil reservoir, it is urgent to get the development pattern transform so as to keep the continuous oil production. In order to further improve the heavy oil recovery rate, the author draw lessons from the successful experiences of steam drive home and abroad and make reference to the criterion of steam drive selections, make use of numerical model and physical model, give the comparisons and analysis based on the pilot test results of steam drive in Sha3 layer, propose that steam drive has relatively technique advantages of sweep efficiency and ultimate recovery factor at current oil price. The initial 6 well groups with steam drive treatment can improve oil recovery ratio of 14.6%, and 2.63×10~5 tons for incremental recoverable reserves. It is therefore to know that steam drive is the feasible technique of Sha3 layer of Block Wa38 development in future.The main researches include the following aspects: fine geologic research on Sha3 layer of Block Wa38, evaluation of huff and puff efficiency and analysis of waterflooding pattern, current problems and potentials at present phase, pilot test results of steam drive treatment in Sha3 layer, reasonable development pattern optimization, petroleum development program of steam drive, economical evaluation etc. The research work of this paper could provide the basis for reservoir development pattern transform, and is also a beneficial exploration to deep zone development of extra heavy oil reservoir with huff and puff at last stage, giving a guidance and reference to the similar reservoirs home and abroad.
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