Abstract Steam huff and puff, generally thought of as a single well process, has seen interwell interactions such as steam channeling and/or watering out of neighboring producer by condensed steam at the later stage resulting in the poor production performance.
In contrast to the single well huff and puff (also named CSS), sequential multi-well steam huff and puff (SMWSHP) is a method in which some wells go to injecting, soaking and producing sequentially or at the same time. This method could avoid steam disturbance and interwell channeling and improve the production performance of huff and puff.
Feasibility study on sequential multi-well huff and puff in developing heavy oil reservoir is presented in the paper. The mechanism and sequence (manner and overlapped time) of SMWSHP and also the pilot test have been studied in a heavy oil reservoir from Xinjiang Oil Field. Both the field pilot test and the theoretical study show that SMWSHP could economically prolong the production period, improve the production performance of steam huff and puff, and increase the oil recovery by 5∼7%. The mechanisms of SMWSHP are as follows:Injecting steam into several wells at the same time can avoid the interwell steam channeling, extend the heating area and increase the reservoir pressure.
Injecting steam in various sequences could displace oil into different direction and so, improve the sweep efficiency.
Introduction Steam huff and puff (also named cyclic steam stimulation, CSS), generally thought of as a single well process, has seen interwell interactions such as steam channeling and/or watering out of neighboring producer by condensed steam at the later stage resulting in poor production performance.
Heavy oil has been produced from A-1 Block, Xinjiang Oil Field for many years. Now, steam huff and puff has entered into later stage, characterized by low pressure, low oil production and so, poor recovery results.
In order to improve the development result of huff and puff, sequential multi-well steam huff and puff (SMWSHP) is applied to produce oil of A-1 Block, in which, in contrast to the single well CSS, a group of wells go to soaking and producing sequentially or at the same time. This method could avoid steam disturbance and interwell channeling and improve the production performance of huff and puff.
Both the field pilot test and the theoretical study show that SMWHP could economically prolong the production period, improve the production performance of steam huff and puff, and increase the oil recovery by 5∼7%
Up to the end of 2004, SMWSHP have been carried out in more than 1,000 wells in PetroChina Company Limited (PetroChina), the largest petroleum company in China, and have increased production by 100,000 tons and economic profit by more than US$20,000,000.
Geology There are two sands in A-1 Block, which are Keshang Sand (T2k2) and Badaowan Sand (J1b). The Keshang Sand, the primary producing zones in A-1 Block, is in the upper portion ofKe-Wu fault zone ofZhunger Basin. The structure is a monocline with dip from 3º to 10º. The depth of Keshang zone is from 350m to 600m. The porosity of oil formation is 18∼31% with the average of 23%. The permeability is 20∼1460×104µm2 with the average of 362×104µm2. The oil density in the reservoir is 0.8925g/cm3 and live oil viscosity is 2000mpa.s. Table 1 shows the details of reservoir properties of A-1 Block.