Study On Well Test And Application Of Sandstone Gas Reservoir In Sebei Gas Field

Sebei gas field is typical of layered sandstone gas reservoir, featuring in shallow reservoir, long gas well, large amount of gas layer and complex distribution of gas water, so multilayer commingled production is mainly adopted for the production of it. Currently single well test model has been generally used on site to explain the data analysis of test well, which ignores the effect of multilayer characteristics, leading to wrong interpretation results. Therefore, in order to improve the reliability of well test interpretation, nearly4years of well test pressure buildup curves of Sebei gas fieldf have been analysed in this paper. As a result, two main characteristics of the curves were gained:(1) generally no unit slope straight line in early period;(2) the pressure derivative curve goes commomly upward in the middle and later period. According to the analysis, three kinds of multilayer well test interpretation models suitable for the actual characteristics of Sebei field have been established:multilayer homogeneous gas reservoir model without fluid channeling, multilayer composite gas reservoir model without fluid channeling and two-layer gas reservoir model considering fluid channeling. Based on the analysis of the three kinds of multilayer gas reservoir well test model theories and type curve, the influence law of multilayer characteristics on well test curves was obtained,(multilayer characteristics include layer, interlayer flow coefficient ratio, storage coefficient ratio between the layers and the skin factor of each layer, wellbore storage coefficient of each layer, boundary distance between layers/composite radius, interporosity flow coefficient, etc.). Besides, it has been concluded that when there is great differences between layers, using single well test model to explain multilayer gas reservoir can lead to shorter boundary distance and smaller skin factor. On the basis of the above analysis, with the combination of single well test model, well test interpretation results (porosity and permeability) and multilayer well test model, an approximate well test interpretation method of Sebei gas field multilayer gas reservoir was put forward. Through this interpretation method, three typical wells and five instance wells in a layer-group gas reservoir shut-in have been explained by way of living example and reliable results has been obtained, proving the practicability of this interpretation method. A set of well test interpretation methods applicable for the geological characteristics of Sebei gas field have been formed through the study of this paper, which provides support for the development of thoery and technology of actual application and production.