Workshop on Passive Seis mic Limassol, Cyprus, 22-25 March 2009

Passive Seismic Case Study for Hydrocarbon Exploration in South Albania

N. Martakis* (LandTech Enterprise SA), A. Serpetsidaki (University of Patras), G.A. Tselentis (University of Patras) & P. Paraskevopoulos (University of Patras)

Workshop on Passive Seis mic Limassol, Cyprus, 22-25 March 2009

Introduction

The last ten years, Passive Seismic methodology has been accepted by the oil and gas industry as a powerful exploration tool especially for large areas characterized by difficult geotectonic regimes.

This technique has already been applied in oil exploration projects successfully, either as a reconnaissance tool or as complementary method to the existing geophysical data. The 3D P-wave velocity models and Vp/Vs ratios that can be derived directly from processing of microseismic data can provide significant structural and lithological information along with information about fault and fracture characteristics in the area of interest.

In this presentation we are going to describe the application of Passive Seismic methodology in oil and gas exploration in South Albania. The results presented in the abstract are referred to the first 3 months of operations in the area, but Landtech has the permission by Stream Oil and Gas Ltd to present more detailed data after the end of the project (February 2009). The main target of this survey is the mapping of the deep evaporitic structures that caused severe penetration problems to the conventional seismic and generally to provide structural and lithological information for the area of interest, useful for further development.

Microseismic Network

The selected area for the tomographic inversion is localized in the south-western part of Albania and spans 20x40km2 (Fig.1).

Figure 1: Seismicity recorded by USGS since 1973. Gray rectangle represents the project’s study area.

A microearthquake network consisting of 39 EarthData PR24 stations supplemented with LandTech LT-S01 three component velocity sensors deployed during the experiment, which began on 12th of January 2008 and will be completed after 12 months. We attempted to deploy the network over a grid with an average spacing between nodes of 5km (Fig.2). In the

Workshop on Passive Seis mic Limassol, Cyprus, 22-25 March 2009

last 5 months of the recording period has been decided to install 30 stations more in order to densify the network within the target area.

Figure 2: Distribution of seismic stations installed in the area for the Albania project (gray area in Figure 1)

Data Analysis

For the recording period of the first 3 months, 495 events were located within or close to the area of network. The 375 events with the highest quality were used in tomographic inversion procedure. The criteria we used for selecting the best located events were:

• Location within or maximum 10km away from network

• RMS error less than 0.20s

• ERH, ERZ less than 500m

• At least 10 P & S wave arrivals

The magnitude range for most of the recorded microseismic events was from 0.3-3R and their hypocenters were located in depths less than 10km. A map with event locations and 3D distribution of hypocenters are presented in figure 3a and 3b.

Workshop on Passive Seis mic Limassol, Cyprus, 22-25 March 2009

(a)

(b)

Figure 3. (a)Distribution of seismic events recorded within 3 months in South Albania (b) 3D distribution of microearthquakes

Tomographic results

After data processing 375 seismic events were selected for the tomography inversion with 9347 P&S arrivals. The figures presented below (Fig.4) are only part of the preliminary results of this project and show P-wave velocity plane sections at different depths. Final velocity and Vp/Vs model along with interpretation and correlation with well data will be available after the end of the project (February 2009).

Workshop on Passive Seis mic Limassol, Cyprus, 22-25 March 2009

Figure 4: Tomographic results for P-wave velocity at different depth layers.

Conclusions

After the first 3 months of recording in South Albania, 495 microseismic events were located within or close to microseismic network consisting of 39 stations. Taking into consideration that the monitoring period will be 12 months, more than 1500 events are expected to be recorded and more than 30000 P & S arrivals are going to be used for tomographic inversion. Based on this, our intention is to fulfill project expectations like a detailed 3D structural and lithological description of the study area and mapping of the deep evaporitic structures that are present in the area and have caused significant penetration problems to the existing conventional seismic surveys.

Acknowledgments

Landtech Enterprises S.A would like to thank Stream Oil & Gas Ltd. for the permission to present the results of this survey.