Microseismic Reservoir Monitoring In A Deep Carbonate Wellbore Environment In Kazakhstan
Authors: Maver Kim Gunn , Rinck Uwe , Boivineau Ann-Sophie , Hilsman Y. Gil , Eales Martin , Daley Timothy 
Published: May 2016

The Karachaganak field is a super giant gas and condensate field in North-western Kazakhstan. Karachaganak Petroleum Operating BV (KPO) has deployed an 8-level microseismic sensing system in 2008, with its deepest sensor at 4109 m sub-sea depth to monitor and interpret production-related microseismicity, which can have a significant impact on reservoir management of the Karachaganak Field. An on-site microseismic sensing system is recording microseismic events on a continuous basis. Microseismic events have been located and initial interpretations of the microseismicity will provide valuable input to the reservoir model and should impact how the reservoir is developed.

Introduction

Microseismicity provides continuous real-time information about the stress changes in the reservoir caused by injection and production operations. Mapping these changes in both space and time offers a unique insight into the effect of pressure change on the lithological framework and associated movement of reservoir fluids [1].

Historically, recording and interpreting microseismicity provides valuable information about reservoir performance. With the development of the acquisition technology and processing software, new challenging deployments of microseismic sensing systems are being proposed [2]. Karachaganak Petroleum Operating BV (KPO, a JV comprising Eni, BG-Group, Chevron and Lukoil) believes that the monitoring and interpretation of production-related microseismicity can have a significant impact on reservoir management of the Karachaganak field, Kazakhstan.

The Karachaganak field is a gas and condensate field in North-western Kazakhstan in Lower Permian to Carboniferous carbonates (Figure 1). The crest of the field is at 3500 m with the gas/oil contact at 4950 m (1450 m gas column) and the oil/water contact at 5150 m (200 m oil column). There is up to 5% H2S (hydrogen sulfide) and 5.5% CO2

To ensure microseismic events are recorded and provide reliable reservoir information, the microseismic sensor array has to be correctly designed, be adequate for monitoring in a very deep well and be reliable for long term monitoring. The recorded microseismic data has to be triggered and processed to ensure only events related to reservoir activity are located correctly and interpreted. These challenges are addressed in this paper.

Well Planning

To map microseismic events in a reservoir, a microseismic sensing system is required that can consistently record high fidelity, low-noise data in order to maximize the located event population. The deployment plan, such as a dedicated well or adapted production or injection well, must be decided. System reliability is crucial because many of these systems are permanently deployed.

The design of the microseismic sensing system must be determined including the number of geophones, geophone spacing and deployment depth. Network modelling and survey evaluation software allows the design of a microseismic sensing system to ensure the microseismic event location and source parameter calculation meet objectives. Given certain assumptions, it is possible to make quantitative predictions about the likely performance of a microseismic network and to assess the relative merits of different configurations of sensors to optimize the choice of sensing system.