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The Seria Field was discovered in 1929. Cumulative oil production reached 164X10 6 m 3 (end 1996), approximately 34% of known in-place volumes. A maximum oil production level of 18 780 m 3 /d in 1956 has since declined to 2800 m 3 /d. Most of the more easily recoverable oil has now been produced. Undeveloped oil is concentrated in economically marginal accumulations for which simple subsurface models are an inadequate basis on which to plan further development activities. Instead, dynamic simulation of detailed computer-generated 3D reservoir models is required to optimize reservoir management and evaluate potential development options. 3D seismic data are used to assess undrilled closures and new exploration plays resulting in the development of new hydrocarbon accumulations. Amplitude analysis combined with GST/RST logging has identified areas of unswept oil within the field. Detailed 3D reservoir geological models integrating sequence stratigraphic concepts with reappraisal of core and wireline data are being built using Unix workstations. The models incorporate the results of advanced petrophysical techniques, such as image analysis and resistivity inversion, to quantify net sand, porosity and saturation, and NMR to provide information on moveable oil and permeability. The model forms the input to advanced reservoir simulators where multiple sensitivities can be tested to determine the optimum placement of new wells. Advances in drilling technology have led to the use of horizontal and multi-lateral wells to give the increased productivity necessary for commercial success of such marginal developments. Concurrent engineering effort has led to the field's facilities being rationalized to improve efficiency and reduce costs and the designing of re-usable well jackets for the shallow offshore part of Seria.

The Christmas tree coral Antipathes dendrochristos is a recently discovered black coral species that represents a habitat associated with numerous sensitive taxa in the Southern California Bight. We evaluated whether broad-scale oceanographic features influence coral density and size by selecting from among generalized additive models (for density) and generalized linear models (for size) that represented competing hypotheses. We constructed models to predict coral density and size using depth, seafloor slope, surface primary productivity, bottom currents, ocean temperature, salinity, and dissolved oxygen as candidate covariates. Specifically, we evaluated hypothesized links between pelagic production and benthic coral utilization and between bottom currents and larval coral dispersal. Our analysis revealed that high surface primary productivity in combination with depth and January currents are important predictors of Christmas tree coral density. Higher coral density coincided with greater chlorophyll persistence and optimal depths near 400 m. Surface productivity increasingly was associated with Christmas tree corals at shallower depths. Our results supported the hypothesis that ocean currents affect coral density via larval dispersal mechanisms. The selected coral size models responded to similar covariates, corroborating coral density results. Fish and invertebrate ordinations indicated that Christmas tree corals were widely distributed across environmental gradients and that Christmas tree corals cooccurred with several demersal fish and invertebrates. Several predicted coral hotspots remain unprotected from fishing, particularly in areas adjacent to highly populated portions of the Southern California Bight. These regions should be targeted by future studies to confirm the presence of Christmas tree coral communities and to evaluate their vulnerability.

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