Print this pageBasin-Scale Evolution of Formation Waters revealed from Diagenetic Minerals: Does It Help Us Predict Reservoir Quality?
WORDEN, RICHARD H.
The prediction of reservoir quality is a holy grail that has thus far proved elusive. It has long (though not ubiquitously) been thought that the movement of subsurface waters is the key to diagenesis and cementation in sandstones. This study was initiated to assess how formation water evolves on a basin-scale and what affect the movement of water might have upon reservoir quality. Data from diagenetic minerals in wells across the Triassic of the Paris Basin, France, included fluid inclusion salinity, carbon and oxygen stable isotopes and strontium isotopes and were given a precise age by using fluid inclusion homogenisation temperatures in association with modelled thermal histories.
The results, integrated with a study of produced waters, show that formation water in the basin-centre is saline (>100,000 ppm) with evolved oxygen isotopes and probably has been stagnant for >100 Ma. In contrast, the basin margin experienced a major influx of meteoric water at about 25 Ma. Intermediate areas have undergone partial saline water-replacement. The influx of meteoric water coincided with localised uplift although no part of the Triassic sandstone has been exposed at the surface. The Triassic sandstones have experienced both open and closed water system diagenesis.
Despite the closed-system at the basin-centre, the sandstones are extensively cemented and display a wide range of diagenetic minerals. Diagenetic patterns are replicated across the basin regardless of the type of formation present at the time. The movement of formation water appears to be irrelevant to the evolution of reservoir properties.