Stimulation Experiences in Heavy Oil Exploratory Wells

Arturo Santillán Salazar
Halliburton

Hydrocarbon reserves in Mexico and over the world, are encountered with increasing difficulty for its exploitation or incorporation as a true reserve; deep water, heavy oil, low permeability, etc. So, the application of advanced and adequate technologies plays a very important role.

Crucial part of the reserve evaluation in heavy oil reservoirs, is the way the wells flow, and how productivity conditions are enhanced. In spite of “rate” factor, is not a parameter for determining the recoverable reserve volume, it is a decision factor for deciding whether invest in a project or no. In other words, the velocity of the return of the investment is a determinant factor.

In this poster the experience of acid and non acid treatments is compiled, these jobs were executed to get a better evaluation of wildcat wells in the Campeche sound. The general characteristics of the study cases are as follows:
Permeability – Medium-Good
Low Productivity Index
High Viscosity at reservoir conditions
High Density (8.5 – 11 API)

In the case of heavy oil reservoirs with medium permeabilities, the viscosity is the factor that governs the fluid flow through the rock, remember that viscosity acts as (denominator) in Darcy’s equation for radial flow, the higher the viscosity the lower the rate. In the same sense, the drawdown through the rock also controls the flow; if we modify these parameters it is possible to enhance the productivity indexes for this type of wells.

It is true that viscosity reduction of the reservoir fluid is just performed at a regional manner around the well, but this operation promotes the flow establishment from the formation to the well; in the other hand, the drawdown reduction is due to an increment of the flow area (by means of wormholing o creation of fractures), this situation is similar to have a bigger diameter well. As an additional recommendation the formations must be perforated as long as possible, in order to eliminate partial penetration skin factor, unless the existence of an aquifer prohibits it.

Volume for the treatments must be adecuated, Extended Matrix Acidizing is the desirable type of job, with volumes from 300 – 400 gal/ft, in the case of carbonates, and in sandstone, the use of non precipitating fluids is mandatory. Most of the low pressure wells wont flow, however fluid level maintenance is a desirable situation when the artificial production method depends upon this level, for example electrosubmersible pumping, or gas lift. The practice will guide, to choose deep points of pumping or gas injection.

Selection of treatment fluids, must consider viscosity reduction and promote compatibility, while having enough dissolving power. For convenience, the cases are presented just using the first two letters of the well name, as follows: PO-1, BA-1, NU-1, TS-1. In the poster material particular data of each case is shown, such as, logs, well tests, type of treatment.

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