Exploiting Upstream/Downstream Synergies for Improved Risking of Hydrocarbon Quality and Development Economics in Deepwater Plays

Lloyd M. Wenger¹, Cara L. Davis¹, Clifford C. Walters², Gary H. Isaksen³, and Mark Richardson^3
1 ExxonMobil Upstream Research Company
² ExxonMobil Research and Engineering Company
³ ExxonMobil Exploration Company

Hydrocarbon quality has a major impact on the economic viability of the development of deepwater discoveries. During exploration, accurate and early prediction of hydrocarbon quality, producibility and value is desired to evaluate and rank drilling prospects. Beyond basic concerns of API gravity, viscosity and recovery efficiency, hydrocarbon quality impacts the cost of development infrastructure required to produce, process and transport the hydrocarbons. Early identification of oil quality issues allows the Downstream to develop targeted solutions and prepare refineries for upcoming feedstock changes. Synergies created by "breaking down the silos" and involving all affected Upstream and Downstream organizations from the early exploration phase clearly benefit the integrated petroleum company.

Upstream approaches to pre-drill prediction of hydrocarbon quality typically consider the anticipated source facies and maturity and its impact on generative hydrocarbon compositions and the possible reservoir alteration processes (e.g., biodegradation, phase-separation, and gravity-segregation) that may occur in prospects. Biodegradation is a key control on hydrocarbon quality in many deepwater areas where cool reservoirs are subject to the increased activity of petroleum-degrading bacteria at temperatures less than 80°C. Expected reservoir temperatures are estimated, and correlations are developed to predict API gravity and gas-oil ratio, from which viscosity estimates can be calculated from black-oil models. Models of charge timing and post-charge reservoir temperature history may help constrain hydrocarbon quality predictions; however, experience has shown that the migration efficiency (i.e., access of charge to specific traps) is often the overriding control on oil quality in many deepwater areas.

Gains from Downstream linkages and communications include identification of oil quality issues that impact refining and also may factor into development facilities planning and economics. Parameters of interest to refining include the distribution of acidity throughout the molecular-weight ranges, sulfur speciation, metals content, emulsion-proneness, and de-salting issues. Potential flow assurance problems in well bores and topsides include asphaltene or wax precipitation, inorganic and organic scale, corrosion, slugging, hydrates, foaming, and emulsion breaking. The early identification of potential problems is crucial to realistic assessment of development economics (e.g., may impact tubing alloys and diameters/insulation, use of artificial lift or need for regular pigging) and their anticipated remediation methods (e.g., use of inhibitors/chemical injection) may cause major problems or disruptions at the refinery. The most effective solutions are those that consider bottom-line impacts throughout the value chain and strive to minimize them.

In order to effectively evaluate deepwater development potential, critical samples and data must be collected from the earliest phases of exploration drilling and Upstream and Downstream stakeholders included in evaluation and planning. Appropriate fluid samples must be collected during exploration and fully characterized, including recognition of and correction for drilling contaminants. To assure these samples are taken and appropriate analyses completed requires a corporate mindset that sees beyond the immediate operating business function.

At ExxonMobil, a "Petroleum Quality Simulator" forward model has been developed to draw upon the synergies of the Upstream and Downstream. The simulator links modeling programs from the range of business functions, and provides an integrated tool for making hydrocarbon quality predictions and geoscience model validation. This simulator relies on advanced oil compositional analyses, chemical reaction schemes and physical property models developed for refinery operations with basin generation models and knowledge of geologic and microbial processes that ultimately control fluid properties in the reservoir.

AAPG Search and Discovery Article #90062©2006 AAPG Hedberg Research Conference, Veracruz, Mexico