The recent years have seen extensive putting on stream of wells draining carbonate reservoirs characterized by low reservoir properties. The authors analyze the available data on drilling, completion, and operation of horizontal wells and horizontal sidetracks targeting carbonate reservoirs in Tatarstan’s oil fields. 3D geological and reservoir models based on seismic survey results were built to find sweet spots for horizontal wells in Deposits Nos. 302, 303, and 665 of the Romashkinskoye field and the high-formation-resistivity Kizelovskian reservoirs in the Bavlinskoye oil field. Analysis of Deposit No. 302 wells’ performance has demonstrated that the initial production of horizontal wells is 1.44 times as high as that of deviated wells. No relationship between oil production rates and the working length of the horizontal wellbore was found. Water production starts to increase in the first months after wells have been put on stream and does not depend on the distance to OWC. It was found that one of the reasons of rapid watering is placement of horizontal wells in zones of intense fracturing with high openness of fractures.
As for horizontal wells targeting the Tournaisian formations of the Bavlinskoye field, they produce water-free oil with initial rates 1.7 times higher than deviated wells. Horizontal sections are drilled in the Kizelovskian formation having high resistivity values. It is separated from the underlying low-resistivity water-saturated layer with a tight impermeable carbonate member. Horizontal sidetracks targeting the Dankovo-Lebedyanskian formations (Deposit No. 665 of the Romashkinskoye field) go to water in the very first months after completion. Increase of produced water does not depend on the distance to OWC. Reservoir properties are rather poor; fractures are mostly vertical or low-inclined. Initial production of horizontal sidetracks is comparable with that of deviated wells.
In-depth study of development targets and consideration of all geological and operational aspects will allow optimal placement of horizontal wells and future decrease of the number of unsuccessful wells.
