February 2011

THE WAY OF IMPROVING OIL PRODUCTION:

RESERVOIR PROPERTIES USING COMBINATION OF GEO­STATISTICAL APPROACH & RESERVOIR MONITORING BY 4D MICROGRAVITY

 

University of Indonesia – Student Chapter of Ameri­can Association of Petroleum Geologists was held a short course titled The Way of improving Oil Pro­duction: Reservoir Properties using Combination of Geostatistical Approach in Seismic Inversion & Res­ervoir Monitoring by 4D Microgravity. This course is divided into two sessions. First session presented by Ms. Dyah Tribuanawati (INPEX), and second session presented by Mr. Eko Widianto (Pertamina EPTC).

FIRST SESSION: RESERVOIR PROPERTIES USING COMBINATION OF GEOSTATISTICAL APPROACH IN SEISMIC INVERSION

In this session we learn about the basic concept of Geostatistical & Seismic Inversion and how to use those theories into the Petroleum production system.

Inversion is the process of extracting, from the seismic data, the underlying geology which gave rise to that seismic. Inversion is a non-unique pro­cess and there is not one method which is the best in all cases. There are 3 types of inversion, those are: Band-limited inversion, Model-based inversion, and Sparse-spike inversion. Model-based and sparse-spike inversion gave the most detailed results. Seismic inversion is used to improve the definition of lithology by the resolution of interpretation.

Traditionally, inversion has been applied to post-stack seismic data, with the aim of extracting acous­tic impedance volumes. Another recent develop­ment is to use inversion results to directly predict lithology parameters such as porosity and water saturation. There are two main points which im­portant: Accoustic Impedance Volume and Porosity Volume.

The aim of using inversion is to convert the seismic section to more accurately represent the properties of earth’s layers. In seismic inverse modeling, the pro­cess is reversed. Beginning with the trace, essentially de-convolve it and end up with the reflectivity series. This reflectivity series is then displayed side-by-side as a set of pseudo-acoustic logs, which we can then interpret as a cross-section of the subsurface in terms of its acoustic impedance distribution.

From this method, we will find that inversion of seis­mic data to impedance could improve exploration and reservoir management success, producing more hydrocarbons with fewer, more highly productive wells. Among the improvements are:

1. Higher resolution through reduction of the wave­let effects, tuning and side lobes.

2. Incorporation of low frequencies not contained in the seismic data.

3. Increase asset team interaction through the use of layer based (versus interface) acoustic imped­ance models that are readily understood by all asset team members.

4. Accurate rock property modeling, as impedance can be related to several key rock / petrophysical properties such as porosity, lithology and water saturation.

When the seismic inversion cannot be used to extract the seismic data, we can use Geostatistical method to solve that. Geostatistics provides a toolbox for the geologist to use in analyzing data and transferring such analysis and interpretation to the task of res­ervoir forecasting. There are four steps for statistical tools, they are:

1. To quantify the spatial continuity of the well data using Variogram Analysis.

2. To find and quantify a relationship between well and seismic data.

3. To use what has been learned to grid the well data using the seismic data as a guide via Kriging with external drift.

4. To assess the accuracy of the map just made.

In conclusion, we know that Geostatistic is used to be applied to quantitatively relate well and seismic data, assess the quality of the resulting map, and estimate the probability of success from the avail­able data.

SECOND SESSION: RESERVOIR MONITORING BY 4D MICROGRAVITY                      

There are 6 contents that will be explained in this session. Those are Introduction to E&P activities, exploration phase, development and production phase, time-lapse technology, 4-D Microgravity and Fluid Movement in Reservoir, and case study: Car­bonate reservoir.

EP will be success in oil & gas industry if using these four main points (high concept, high technology, high cost, and high risk). Petroleum activities phase involves exploration phase and also development & production phase. Reservoir monitoring is one of the solutions in developing and optimizing the oil production. 4D Microgravity is one of the methods which usually did.

Basically, 4D Microgravity is a method which annu­ally monitoring the reservoir’s density changes. Its changes could be identified by re-injecting water or steam into the reservoir then analyzing its density, this procedure usually did once a year. Since the production phase is still working, its density pos­sibly changing due to time. This changes should be monitored by the Geoscientists, so that the EP companies could avoid drilling the reservoir which noneconomic anymore.

In conclusion, the objectives of 4D Microgravity study are:

1. To understand the reservoir heterogeneity.

2. To delineate fault structure and compartmental­ization.

3. To identify of by-passed oil.

4. To understand the re-injection impact, consists of: Lateral movement of injected  water, Water front of injected water, Reposition of injectors (if necessary), and Locating the additional injectors.

5. To help upgrade reservoir models.

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