A New Method for Predicting Interwell Remaining Oil Distribution in Multilayer Sandstone Reservoirs at High Water Cut Stage

Abstract

Since the remaining oil distribution is characterized by scatter and complex in multilayer sandstone reservoirs at high water cut stage, a new method is put forward in this paper to predict interwell remaining oil distribution by using cores, logging data, geologic model and production testing data. Firstly, the interwell sandbody prediction model are set up to predicte interwell sandbody thickness and sedimentary microfacies by using geostatistics and stochastic modelling methods. Secondly, the remaining oil prediction models of various reservoirs are set up by combining the expert system and neural network based on the comprehensive analysis of the relationship between watered-out degree and influential factors in various layers of inspection wells and separated layer testing wells. These factors include sedimentary microfacies, sandstone thickness, structural pattern, communicating states of sandbody with surrounding water injection wells, and injection distances, intensity of water injection, injection-production relationship. The above-mentioned models are used to predict the interwell remaining oil distribution of each layer. This method has been successfully applied in predicting the remaining oil distribution before drilling the tertiary infilling wells in Xing 1–3 area of Daqing oilfield. About 100 layers are studied in this pilot area and maps of remaining oil distribution in each layer are worked out. In addition, the distribution map of remaining oil sandstone thickness in this pilot area is also drawn up and the potential area of remaining oil is pointed out. This method has been used in 28 infilling adjustment areas in Daqing oilfield and good results have been received. By checking 208 layers of 3 newly drilled inspection wells in these development blocks, coincidence rate of single layer predicting remaining oil is at the range of 81%~84%. This paper explores an effective way to study interwell remaining oil distribution in multi-layer sandstone reservoirs. Introduction The underground oil and water distribution becomes more complex with the water cut rises in Daqing oilfield, it is more difficult for the oilfield to recover the remaining oil. The main purpose of the oilfield development and adjustment at the high water cut stage is to recognize the remaining oil and to produce them1, the difficult point is to determine the space distribution of the remaining oil. Thus, the study of the remaining oil distribution is the important subject during high water cut development stage. Since there are many complicated factors effect the remaining oil distribution and not all the layers have the monitoring data, there is a great difficulty for studying the remaining oil distribution in the multilayer sandstone reservoirs at high water cut stage. On the basis of analyzing the geological and the development factors which effecting the remaining oil distribution, the waterflooding data in the inspection wells and the data of the separate layer oil test of the recent years are used, combining with expert system and neural network, an effective method of determining the remaining oil distribution in a single layer by using expert neural network technique is put forward which is applied to the remaining oil potential study for the third infilling adjustment at late period of high water cut stage in Daqing oilfield. Setting up an Interwell sandbody prediction Model Based on the sedimentary microfacies study, using all kinds of geological statistical method predict interwell geological parameters, such as the reservoir thickness. Using facies mode predicting method to predict sandbody boundary in different sedimentary microfacies The facies mode predicting method is guided by every sedimentation model and sedimentology and based on a large quantity logging data to reasonably predict plane combination characteristics of all kinds of sedimentary microfacies in the reservoir.

Wygd Study on prediction method of drilling pressure in low permeability oilfield

“…According to the percolation formula, the block average well spacing, well diameter, well depth, well flow pressure and other single well parameters are used to form a fast calculation chart and calculation method for formation pressure and pressure coefficient [16] . Based on the research results, a drill-in boundary chart with well spacing [17] , reservoir permeability and cumulative injection-production ratio as variables is formed to calculate the distance, pressure, time and other boundaries under different parameters [19] . Fig.…”