Fracturing Technology Study Of Thin And Poor Quality Pay Zones

Contradiction of unbalance between reserve and production is being gradually predominant after Daqing oilfield enters into a stage development of extra-high water-cut oil exploration. Fracturing technology is one of the most efficient means to explore the oil reserve with low permeability, oil immersion, oil patch and oil trace. Space distribution of this reservoir is very complex. In plane view some pay zones of the reservoir have been water-flooded or they border high water-cut zone, some lie in the bad place of main layer, and some are scattered individually. In vertical view, target stratum is dispersed inside each oil layers, and distributed between high water-cut layers. Barriers between oil layers and water breakthrough layers are very thin, and the gap is only approximate 0.4 m.For such condition aforementioned as thin oil-layer barrier, its adjacence to water-cut layer, and its poor dispersion and physical properties, current fracture technologies are confronted with many new problems as follows.Nowadays, the lower limit of the barrier for fracture technologies is 2.0 m. Because the poor and thin oil layer is close to the high water-cut layer layers and the barrier is less than 2.0m, current fracture technologies can not be appropriately applied. Otherwise, barrier cross-flow may cause move-up of water content.Due to the poor physical property and large magnitude of thin pay zones, it is very difficult to apply fracturing remold. Distances between two packers which fracturing technology requests is less than 40m. Target stratum of thin and poor quality pay zones distributes irregularly and oil layers space is over 40m. Therefore, efficiency is low and cost is high if these oil layers are fractured one by one. In practical production, these layers are not fractured and exploited after conventional perforation. Reserves of these reservoirs can't be produced by method of conventional perforation because oil layers'permeability is only 20md and thus water drive energy exists.Therefore, fracturing Technology for thin and poor quality pay zones is developed. High water-cut and large space reservoir can be exploited by this technology and technical support for maintenance can be provided as well.In this paper, we establish strained-condition predicting model for the force state of borehole and matrix material nearby. By using finite element software, constrained characterization and matrix consequence analysis of horizontal fracture are completed, especially for consequence analysis of the joint state between rock and cement mantle interface around fracture. Mechanism of barrier channeling, principle of balance protection and the lower limit of thickness of barriers are defined. Hereby, several balance protection solutions are proposed by developing balance protection packer, pressure transmitting & balance protection packer, balancer, balance sand-blaster and the other auxiliary tools.In the meanwhile fracturing technology of retrieval bridge plug and auxiliary tools are also developed to meet the requirements of large span of thin and poor quality pay zones, high proppant concentration and low displacement & extrusion.In-house testing and field application shows that this technology has advantages of easy operation, low cost and high success opportunities. A lot of reservoirs, which can't be exploited due to the limitation of barrier thickness and distance between two packers, can be re-exploited. The outlook of the application is very optimistic for the current and subsequent oil exploitation.