Abstract

A mature area located in Western Venezuela is enclosed by three main fields, all of them in advanced state of depletion based on the way they have been exploited up to now since 1930. These heavy oil fields have a crude that ranges from 10–14 °API, a viscosity between 1000 and 25000 cp and cyclic steam is the way of stimulation as an standard process for all the new wells and the workovers. Cyclic Steam is becoming less efficient after three cycles application, the steam to oil ratio (<5), which is too low for these fields. Since before reaching this value it used to be around 30–40 for the first three cycles, which is considered a good value. Considering that the oil in place is more than 20 billions barrel of oil and only 23% has been recovered beside the latest static models show that several of the sand bodies has not been drained out as yet. A different strategy or a new plan for the redevelopment of the area is necessary in such a way that the exploitation of these fields could be extended for twenty or more years. This study shows that with good static and dinamic models a reassessment of the whole area can be done, by ways of dividing into regions the fields and applying different producing technologies, some of these technologies are thermal recovery methods as cyclic steam, steamflood, SAGD, electromagnetism and Combustion. All of this will increase the recovery factor up to 80%. The non drained sand bodies could be stimulated by applying cyclic steam in areas of the field with good thermal communication. These are candidates for steamflood and in the areas with clean sand bodies up to 40 ft. Thick, SAGD can be applied. Finally the very depleted reservoirs with low pressure and clean sands are the best for either dry o wet combustion.

Introduction

These heavy oil fields are located onshore on the eastern side of the Maracaibo Lake. They have an extension of almost 80 kms. long by 30 kms. wide. There are three main fields with the gravity of the crude ranging from 10 to 14 °API. These fields have been producing for almost 40 years now. Several of the reservoirs in these areas are in the stage of maturity or declination. The OOIP is 38 billions barrels with a recovery factor of only 22%. There is a need to increase the recovery factor by at least 25% more. The continous increase in the service cost for workovers, the need to look for an alternative to cyclic steam the wells in the mature reservoirs, the need also to improve the efficiency of the huff and puff process and the important remaining reserves to be recovered, all of this show the real need to look for new technologies in order to meet these challenges.

Reservoir Characterization

The producing formation in these fields is called Lagunillas Inferior of Miocene Age. A sequence stratigraphy analysis as illustrated on Figure 1, shows the pattern of sedimentation for the genetic units. As it can be seen there are three compartments (C1,C2 and C3) interpreted on the last integrated reservoir study. These sand bodies are separated by subtle shale strikes and some of the compartments have limited lateral extension. Each compartment has three different ranges of permeability:

  • Low < 100 md

  • Intermediate 200–800 md

  • High > 1000 md

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