Understanding Fluid Phase Using A Seismic PVT Chamber

Abstract

Abstract As oil fields produce liquids (oil or gas/condensate), they undergo pressure change, with the pressure reducing as a function of production rates. Equally, the high production of water from a reservoir can cause major reduction in pressures of gas fields resulting in an increase in the gas cap size and a consequent loss of gas to the surrounding formations. The injection of water or CO2 into reservoirs or underground storage areas causes an increase in local pressure which in turn, has the potential to cause local increases in permeability in the reservoir or at the storage site. Time-lapse three dimensional (3-D) seismic methods are used to monitor the fluid movement during both fluid extraction in producing fields and injection of water or CO2 for EOR or storage purposes. However, little is understood about the seismic effects caused by variations in both pore pressure or rock matrix stress as a result of these operations. During 2003, a low pressure/volume and temperature (PVT) chamber was built at Curtin University to simulate such effects, and to establish the seismic reflection response under these variations. Past research has shown that variations in pressure can cause tuning effects which appear to be identical to bright spots occurring. In that research, it was shown that a variation in pressure causes a change in formation density which can cause a rotation of the AVO fluid line, and this highlighted both the fact that this attribute can be used for sensing variably pressured compartments in 3-D data (missed pay zones) as well as indicate that a bright spot is not always gas-associated but can be pressure-associated in a producing field. This paper discusses the development of this research and the applications of this unique PVT chamber.