Contemporary Airborne Geophysical Methods for Hydrocarbon Exploration
Pavel S. Babayants, R. S. Kontarovich, and V. E. Mogilevskiy
Aerogeophysica, Inc, Moscow, Russia.
Employing of remote geophysical methods, such as airborne gravity and magnetic, at early stages of oil and gas exploration allows increasing significantly the efficiency of exploration works. As the most perspective territory of possible hydrocarbon deposits can be considered the regions of artic shelf. However, these regions still weak investigated, and their huge space and out-of-way situation necessitate the use of airborne geophysics.
Airborne magnetic has been operated in large volume, and now it is traditional well-known method. The airborne gravity is in a quite different situation. This method has been employed for commercial surveys relatively recently. There is intense interest in this method in world exploration industry. It has the doubtless advantage over traditional ground gravity measurements. To day only several countries, including Russia, posses such survey technologies.
The main problem, arising during the gravity measurements from aircraft, is elimination and/or estimation of caused by aircraft accelerations errors that can a tenths thousand times exceed informative signal. This is a task for all components of survey: equipment design, measurement method, data processing procedures.
The airborne gravity measurements can be realizable only with synchronous, non-inertial determination of aircraft path (accelerations). To-day the GPS data is used for this purpose that contributed to advance of airborne gravity in the last years, in spite of the rigid requirements to navigation information. Besides the aircraft position, determination of aircraft velocity and disturbing accelerations are required as well. To meet these requirements it is necessary to apply to data the differential correction with use of base station measurements.
The airborne gravity surveys in Russia are carried out with one of the best in the world developed in Russia airborne gravimeter, extensively used by leading western companies and known in the western market as gravimeter GT-1A. Used in the survey fixed wing aircraft AN-30 (AN-26) allow to execute the survey with speed of 300 km per hour. Under the projects when the large-scale survey (1:50000) is requited, the data can be obtained from helicopter MI-8 at speed 150 km per hour. The survey altitude is minimal with consideration of flight safety.
Some gravity projects: In 2005-2008 Aerogeophysica Inc. obtained airborne gravity data along laid pipeline East Siberia - Pacific Ocean. For the only four years, gravity data was obtained from survey area of 300000 sq.km (area of Ukraine, for example, is 600000 sq.km). Bouguer anomaly maps were created with error 0.5 mGal. In April-June 2006 for the firs time in Russia Aerogeophysica completed integrated gravity/magnetic survey (AN-26 two engines plane) over central zone of Sea of Okhotsk.
In this the differential mode of GPS system operation based on information from three signal reception stations located in Magadan, Okha (Sakhalin Island) and Ust-Bolsheretsk (Kamchatka Peninsula). The distance between survey aircraft and base stations was up to 700 km. Mean-square deviation of re-flight anomalies from mean value is 0.41 mGal. It is important result since the remoteness from coastal stations considered as the limitation of possibility of airborne gravity measurements. Thus, the total Russian zone of Arctic Ocean is accessible for airborne gravity surveys.
AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia