Abstract

Fan-deltaic environment offers a particular challenge for geostatistical modelling. Over the past decades, geostatistical methods are widely accepted and applied to simulate sedimentary microfacies. In this study we have selected Sequential Indicator Simulation (SIS) to generate our model and perform sensitivity analysis. Luanping fan-deltaic outcrop has been selected as a case study. The outcrop is located in Hebei province, China. The main outcrop cut by road is an excellently exposed study area, whose length and height are 1300 meters and 230 meters respectively. The orientation is nearly east-west. It was deposited from upper Jurassic to lower Cretaceous. Based on outcrop studies, 16 types of microfacies have been classified and for simplicity, they have been finally combined into 6 types of microfacies in stochastic simulation.

The 2-D grid of 470×290 (?X=2.5m, ?Y=0.8m) has been designed to establish a single deterministic (prototype) model of Luanping fan-deltaic outcrop. The model honors all existing data and represents a realistic geological interpretation as closely as possibly. The input data of SIS are extracted from prototype model at different well spaces of 100,200,300,400 and 500 meters. As a result, microfacies simulations are constructed under different well spaces. Comparing these simulations with prototype model, prediction accuracy and uncertainty analysis are presented in this study.

The study shows geostatistical tools can well reproduce prototype model of Luanping fan-deltaic outcrop. The prediction accuracy is largely relied on variogram model and proportion of each microfacies. Moreover, SIS can also reflect the microfacies distribution law of fan-delta, especially fan-deltaic plain can be reproduced under less information. Finally the results are applied to NY oilfield, China successfully.

Introduction

During the last 5 years, RIPED, CNPC has been actively engaged in detailed Luanping fan-deltaic outcrop studies. The objective of this project is to develop a comprehensive, multidisciplinary and quantitative characterization of a fan-deltaic reservoir to allow realistic interwell and reservoir-scale models to be developed for improved oilfield development in similar reservoirs in China. Understanding reservoir heterogeneity is the key to increasing oil recovery from existing fields. Oilfield development demands generation of the best possible predictions of production profiles and the best possible basis for well/drainage strategies etc. Moreover, fan-deltaic reservoir is one of the most important reservoirs in China. However, It is difficult to buildup detailed and reliable fan-deltaic reservoir models based on available information using conventional methods.

A number of geostatistical methods have been used in reservoir modelling. Although these methods enjoy wide acceptance, they have rarely been tested with realistic reservoir models. One of the reasons for this is lack of exhaustive quantitative data.

In order to solve above problems, some scientists from RIPED, CNPC have put a lot of efforts into Luanping fan-deltaic outcrop studies for several years.

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