Evaluation of Treatments for Control of Fines Migration in the Ceuta Field in Venezuela
Authors: Colmenares F.J. , Padron A. , Ben-Naceur K. 
Published: December 2007

Abstract

In the Ceuta field, an area located in Lake Maracaibo and assigned to Maraven, S.A. (a subsidiary of PDVSA) for exploitation, there has been a significant production decline during the producing life of wells. Production has dropped from 2000 BOPD to 50 BOPD in 10 months. HCl and HF stimulations have not been successful in restoring the lost potential.

Flow tests and the mineralogical analysis of cores from the area have shown that there is a very high content of fine clastic material, which has a very special characteristic: it moves through pores. When this material finds very small pore spaces, then it plugs them, which results in reduction of formation permeability.

In order to be able to control this problem and restore the permeability of the damaged formation, matrix treatments with Fluoboric Acid (HBF4) have been applied in several wells located in the Ceuta field. These treatments have made it possible to stabilize the clastic material. After the treatment, well production has remained stable for more than four years, and the average gain has been 1500 BOPD/well.

This paper is about the experiences and results obtained during a pilot test involving 5 wells.

Introduction

The Ceuta field is located in the southeastern area of Lake Maracaibo. Its production potential is around 70.0 MBOPD of net oil (37 API). This production potential comes from reservoirs belonging to the Misoa formation from the Upper and Lower Eocene B and C. This potential has been impaired by formation damage which, as proven, is due to fine migration.

Flow tests and the mineralogical analysis of some cores from the area have shown that there is a high content of clay particles such as kaolinite and "Mixed Layer" illite, which have a very special characteristic: they move through pores. When this material finds very small pore spaces, it plugs them, which results in the reduction of permeability in the medium.

In order to control this problem and restore the permeability of the damaged formation, matrix treatments with fluoboric acid have been applied in several wells located in the Ceuta field. These treatments have made it possible to stabilize these migratory clays, and production has remained stable for much longer, as compared with the results obtained when the traditional formulation was applied (12% HCl +3% HF).

The purpose of this report is to share Maraven's experience involving the matrix treatment of formations having this fine migration problem.

WHAT ARE FORMATION FINES?

Fines are solid particles clinging to pore walls in rocks. These particles are produced "in situ" or due to field operations. Fine migration takes place when these particles come loose from the grain surface and they are dispersed and flow through the porous medium towards very small pore spaces, where they build up. This results in severe plugging and consequently, reduction of permeability in the porous medium (Ref. 1).

epending on grain size, fines are classified as Colloidal fines (&lt;2 m), which are influenced by Brownian diffusion and electric double-layer effects, and the Non Colloidal fines (2 to 40 m), which are affected by hydrodynamic forces.