APPLICATION OF VERTICAL SEISMIC PROFIILING TO DEVELOPMENT DRILLING IN THE MOONFIELD, PALO SECO AREA

LINDY PHILLIP
Trinidad and Tobago Petroleum Co. Ltd.
Santa Flora, Trinidad.


As the exploration for hydrocarbons and the development of existing oil gas field continue in Trinidad, as elsewhere, it is becoming increasingly difficult to tap and recover the remaining reserves. This situation requires the application of new and improved technology especially in areas of complex geology. In Trinidad, Vertical Seismic Profiling (VSP) has been applied, to development drilling for the first time on land, in Trintopec's Moonfield, Palo Seco area.
The Moonfield area is situated in west Central Palo Seco, south of the Los Bajos Fault on the southern flank of the Erin-Siparia Syncline. The area is underlain by a sequence of complexly faulted, interbedded sands and shales decreasing in age from the Cruse and Forest to the Morne L'Enfer Formations. Drilling in the Moonfield area has generally been difficult, costly and hazardous due to the high pressures encountered in the low velocity over-pressured shales.
The PS 1387 well was drilled to test the Middle Cruse Sands which are productive elsewhere in the Moonfield area and the Palo Seco Field. The CR-5 Sands, the main target, were well-developed but water-bearing in this well. The purposed of the VSP was:

1. To evaluate the structure for possible fault separation 1387 and the rest of the Moon field area.

2. To delineate the reservoirs and deter mine the remaining prospective acreage of the CR-5 Sands.

3. To identify the over-pressured shales, to assist in effectively designing casing programmes.

In this context two (2) vertical seismic profiles, a zero offset (114.1 feet) and a 'non-zero' offset (5020 feet), were recorded. A gimballed three-component downhole geophone and two (2) airguns were used in the acquisition. The wavefield was separated into its compressive (P) and shear (5) wave components by vector wave analysis before further processing. Inversion of the VSP data (Pwave only) was undertaken and acoustic impedance
surface noise, temporal and spatial sampling, the objectives were realized and resulted, not only In valuable first hand experience in VSP acquisition, processing and interpretation, but the successful drilling of the PS 1396 development well, in an adjoining fault block. In addition, the Interpretation of the acoustic impedance logs assisted in accurately predicting the depth at which PS 1396 would encounter the low velocity over-pressured shale.

Home | About Us | Links To The World  |  Publications | Upcoming Events |

Feedback | Executive Members | Geology |Teaching Resources| Virtual Field Trip

THE GEOLOGICAL SOCIETY OF TRINIDAD & TOBAGO
P.O. Box 3524, La Romain, Republic of Trinidad and Tobago, W.I.