Rio Vista Gas Field

The remaining 18 were run by several smaller operators, including Towne Exploration, Royale Energy, and Tri-Valley Oil & Gas.

Most of the land area within these islands – much of which is below sea level – consists of agricultural fields protected by levees constructed in the late 19th and early 20th centuries.

Drilling and maintenance pads for the gas wells are interspersed among agricultural fields, recreational areas, vacation homes, and waterways.

[6] Climate in the area is subhumid with hot, dry summers and cool, rainy winters, with all precipitation occurring as rain.

Drainage on the field is poor except in the Montezuma Hills, in which it is to the south and southeast towards the Sacramento River via ephemeral streams which dry up completely in the summer.

[7][8] The Rio Vista field is within the Sacramento Basin, a large structural trough between the California Coast Ranges and Sierra Nevada, filled with up to 40,000 feet (12,000 m) of sediments deposited over tens of millions of years.

Wide variations in porosity and permeability within these sedimentary rock layers, along with abundant structural and stratigraphic traps, have allowed for the formation of numerous natural gas reservoirs in the Basin.

Vertical offset along the Midland Fault of the Domengine Formation, one of the major gas-bearing rock units, is up to 500 feet.

[19][20] Because the largely depleted field contains one of the biggest potential underground gas storage reservoirs in the region – 3.6 trillion cubic feet (100 km3) of gas filled a lot of pore space in the source rocks – the field was part of a regional study done by the California Geological Survey to assess the potential value of the area for carbon sequestration.

Several gigatons of carbon dioxide could conceivably be pumped into the depleted reservoir, serving three purposes: 1) to offset atmospheric emissions; 2) to assist in natural gas recovery, by increasing reservoir pressure; and 3) to mitigate subsidence of the overlying land, which is slowly collapsing into the vacated space, as is common over depleted petroleum fields.