Research And Application On Gravity Water Drainage Assisted Steam Flooding In Block Wa 59

Formation S3 of Block Wa59 is a structurally-controlled massive thick super deep super heavy oil reservoir with edge and bottom water. The block was put into production by CSS(cyclic steam stimulation) using a square well pattern with the well spacing of 100 m in 1997. By September 2009, some development issues such as high degree of reserve recovery, high huff & puff cycles, low cyclic oil/steam ratio,serious lifting difficulties due to low reservoir pressure had appeared, making it extremely urgent to convert the development mode. However, the existing mature key techniques, such as steam flooding, SAGD, hot water flooding are not good candidate methods for developing this block. The gravity water drainage assisted steam flooding technique is a new EOR technique for deep super heavy oil reservoirs following CSS production and it is created by Liaohe Oilfield Company.Based on the reservoir features and development situations, the well pattern, well spacing and injection and production parameters for the gravity water drainage assisted steam flooding in Block Wa59 were optimized, and the timing for converting to steam flooding was studied. After numerical simulations, the spacings between the horizontal injectors, horizontal producers and vertical producers were determined.Combining numerical simulations with the geologic development features of the reservoir, three types of well pattern were designed:(1) the horizontal injector facing directly downwards the horizontal producer with lines of vertical wells;(2) the horizontal injector obliquely crossing the horizontal producer with the vertical wells forming homocentric squares, and(3) the horizontal injector paralleling the horizontal producers with lines of vertical wells.Based on the design requirements of the gravity water drainage assisted steam flooding in Block Wa59, researches on steam injection, lifting, monitoring and supporting techniques were also conducted. The issues such as great heat loss in the wellbore of injectors, difficult high – quality steam injection, even producing of the horizontal interval were resolved by using steam/water separators, high efficiency heat insulation pipestring, heat insulation by annulus nitrogen injection, dual-pipe steam injection and steam injection at multiple locations. The lifting methods for the gravity water drainage assisted steam flooding in Block Wa59 were optimally selected,overcoming the difficulties such as deep burial depth of the reservoir, largedisplacement, and high temperature, ensuring the effective water drainage of the horizontal producers, and reducing the pressure and providing the space for the expansion of the steam chamber.The gravity water drainage assisted steam flooding technique was tested in Block Wa59 in October 2009, and by Dec. 2013, the technique had been applied in 8 well groups with obvious results. The production of the well groups had kept on increasing from the initial oil production of 30/d to 204t/d with the instantaneous oil/steam ratio of 0.23, cumulative oil/steam ratio of 0.16 and incremental oil production of 182,700 t during the period, so the decline production of the block had been alleviated and the recovery of the reservoir had been increased.