Abstract
The reservoir, located in the Sirte Basin, Libya was discovered in the early 1960s. Since then, more than 65 wells have been drilled. By the end of the year 2008, more than 160 MMstb undersatured oil have been produced from the Upper Cretaceous. Water cut has risen to 65% and average reservoir pressure is still 1000 psi above bubble point. The individual well production history is highly influenced by water coning.
The field is geologically complex; heterogeneous, contains numerous large and smaller normal faults sometimes associated with fractures, leading to local permeability enhancements. Average gross thickness is about 300 ft. Recovery is mainly (80%) by the strong edge water influx and by expansion (20%).
The objective of the History Match (HM) was to accurately determine the distribution of the reminder movable oil, in order to enable reliable performance predictions of existing and future wells. To meet this goal, the total amount of produced fluids on a well-by-well basis as well as the average local pressure must be matched within close limits.
Conventional HM techniques failed due to the complex geology and production history. Especially the highly variable water cut could not be matched satisfyingly. For this reason, a new HM method and workflow, called Target Pressure and Phase Method (TPPM), was applied. TPPM ensures, that the calculated average reservoir pressure and the calculated amount of produced liquids match the corresponding measured values at every point in time. This is achieved by regulation of water influx from artificial boundaries and automatic distribution of the inflow along the well trajectories. Thus, the engineer can immediately concentrate on matching the well-by-well performance leading to a considerable reduction in project duration. Additionally, TPPM gave excellent results in HM. Thus reliable future field operation scenarios can be designed and calculated. The presented workflow and method is generally applicable, especially for reservoirs under strong water influx.
