Abstract

This history case discusses a sector the volcanic naturally fractured field in center of Cuba. This field had a complex geologic structure, with vertical productive wells that cross several litology packs (fine, thick tuffs and effusive).

An integral study that examine detailed geology, log and core analyses, well testing, fracture description and numerical simulation using a standard dual-porosity model.

For the representation of matrix-fracture system led good history match for each well.

The conclusion of this work demonstrated that the sector behaves as multi layer reservoir. The profiles of pressure and oil saturation showed, that the studied sector there are areas with productive potential that have not been incorporate to the production.

The methodology used to reach a history match in this case history is presented in detail.

Introduction

The Pina Field is in the Central region of the Republic of Cuba. This field has a complex geologic formation. The developed geologic model shows that the field is divided in 9 blocks by the presence of several faults, the results of well tests, the production geochemistry tests and formation water analysis show that these blocks behave as different hydrodynamic units.

The predominant reservoir in the Pina Oil Field is fracture-porous and in occasions fractured, classified by the Dr. Roberto Aguilera (1) as reservoirs Type BII and C. Technological advancements in dual-porosity system for both well testing and reservoir simulation have allowed both fracture and matrix properties to be quantified.

The field began to produce light oil in June of the year 1990. The production rates were low in their beginnings, influenced fundamentally by damage that was caused to the wells during drilling operations. The employment of the hydraulic fracturing improved the levels of production of the stimulated wells, considerably.

The objective of this work was based on the employ of the numeric simulation to:

  • Confirm the geologic model developed in the most productive block (Block I) in the location.

  • Define the hydrodynamic behavior of the wells in the Block I.

  • Check that a model of double porosity is able to represent the hydrodynamic behavior between the matrix and the fractures in this reservoir.

Geologic Description

This location possesses a complicated geologic formation, with the presence of foldings and dislocations. In the stratigraphic column, the dislocations belong to the Cretacic and to the paleogene occurred several sedimentation cycles, as well as different erosion levels; this location is lithologically characterized by the presence fundamentally of tuffs of different grain and flows of lavas.

Tuffs: they are subdivided in two big packages:

Fine tuffs: formed by cristaloclastic and vitroclastic tuffs of andesitic composition and of fine grain; they are muchaltered to clays their content of volcanic glass. Among the tuffs intercalations of marls appear, shales, sandstone and very occasionally conglomerates of vulcanogen matrix. The thickness of this package oscillates between 400 and 600 meters.

Coarse tuffs: formed by tuffs of andesitic and andesitic-basaltic composition of different grain, prevailing the thick grain, with intercalations of conglomerates, argillaceous limestone and tuffites.

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