Abstract

The potential migration pathways of underground injection control fluids (UIC) from water disposal, water flood, steam flood, and cyclic steam processes in and around oil fields are governed by the subsurface hydraulic gradient field, which is often determined with reservoir pressure measurements. Because public data on these pressures are difficult to obtain, other techniques must be used to estimate the gradients that govern fluid flow. In support of the State Water Resources Control Boards Regional Monitoring Program of Water Quality in Areas of Oil and Gas Production, we present an approach which uses publicly-available well data to map the net difference in injected and produced fluid volume in select oil fields, and identifies possible fluid migration pathways.

To do this, we use California Division of Oil, Gas, and Geothermal Resources UIC injection and produced-water production volume records to create a volume-balance map for select oil fields in Kern County from 1977 to the present. Monthly injection volumes for each individual well are summed, then spread outward from the well location. The same method is used to map the spatial distribution of monthly production volumes. The maps for injection and production volumes are then be superimposed, with the difference yielding the net volume balance and a proxy for pressure gradients. Because this method is based on individual wells, net volume balance can also be mapped by field, pool (formation), or by shorter time periods.

We find that in some pools in Western Kern County oil fields, injection volumes greatly exceeded production volumes, implying fluid gradients that may have driven migration of injected fluids away from the pool. High net injection volumes also are present near the border of some field suggesting displacement of saline fluids already present in the reservoir, possibly into aquifers outside of the field. In other areas, production volumes exceed injection volumes and correspond to the well-documented surface subsidence determined using geodetic methods.