Ordovician reservoirs in Tahe oilfield are typical fractured-vuggy carbonate reservoirs of fossil karst type.Progressive exploration and development pattern was adopted in the initial stage of development.Reserves were brought into production stage by stage.Vertical well pattern combining the selected "spots

lines and the whole area" was applied to control the reserves.Reservoir prediction and identification technologies with extraction and analysis of seismic attribute as the core

as well as strong acid fracturing and sidetrack horizontal drilling technologies were successfully applied in development.Success ratio of development well increased from below 60% to over 85%

discovered oil reserves in place exceeded 500 million tons

and annual production capacity of the oilfield reached 3.5 million tons.However

several factors have influenced further improving development effects along with progress of oilfield development

such as inadequate understanding of the features of fractured-vuggy reservoirs

low reliability of discovered oil reserves

and lack of measures to enhance oil recovery and single well production capacity in mid-and late-development stages.To solve these problems

the following measures should be taken in future oilfield development:(a) compilation or adjustment of development program should be made on the basis of producing reserves or recoverable reserves;(b) enhancing control over reserves by applying combined vertical and horizontal well pattern;(c) redividing development blocks;(d) determining rational well numbers according to single well controlled reserves;and(e) determining individual well's production proration according to rational producing pressure drop.