Abstract

The diagenesis and fluid migration history of the Indian basin field was investigated using transmitted-light, UV-epifluorescence, cathodoluminescence, and SEM-BSE microscopy as well as d¹³C, d¹⁸O, ⁸⁷Sr/⁸⁶Sr, and fluid inclusion analyses. These data show that replacement dolomite and later saddle dolomite cements precipitated after substantial burial during tectonically valved, episodic injection of hydrothermal brines. Vugs and molds were associated with the system of hydrothermal fluid flow, which was driven by convection, probably initiated during 40-30 Ma intrusive activity and continuing after the onset of Basin and Range uplift and unroofing. High quality Indian basin reservoir occurs where Cisco and Canyon Formation carbonates were extensively dolomitized by the hydrothermal system. The distribution of the dolomite and associated secondary porosity was controlled by depositional setting (sedimentary facies and early diagenesis) and proximity to fault or fracture systems that were conduits for hydrothermal fluids. Relatively clean, carbonate sediment deposited in downdip settings was spared early, meteoric diagenesis, and thus, was prone to the development of dolomite and secondary porosity later in the paragenesis. Petroleum and natural gas migration occurred after some Basin and Range uplift, but before regional heat flow decreased and the reservoir cooled to present-day temperatures.