Spontaneous Imbibition Experiments of Enhanced Oil Recovery with Surfactants and Complex Nano-Fluids

Abstract

Two types of porous media were analyzed with the intention of exploring alternative enhanced oil recovery methods. Core samples were taken from the Tensleep Formation of the Black Mountain Field in Hot Springs County, WY. The lithology is mainly sandstone and dolomite. The measured effective porosity values ranged from 13.0 to 18.0%, and permeabilities from 19 to 68 md. Production from the Tensleep and Phosphoria formations using conventional methods has resulted in a low secondary recovery factor, possibly due to high capillary forces and an oil-wet formation. Different surfactants were investigated to determine the viability of a possible enhanced oil recovery process using a spontaneous imbibition process in Amott cells. A very high enhanced recovery factor of more than 89% was achieved using a complex nano-fluid that consists of a mixture of surfactant, solvent, co-solvent and water. These recovery factors compared with 13% by brine imbibition and up to 21% using commercial surfactants. At the other end of the scale, very high porosity volcanic pumice was also subjected to the same tests. For this rock the porosity values ranged from 65 to 90% and permeabilities were 2.0–2.7 d. Secondary recovery showed values up to 81% on spontaneous imbibition and up to 91% when surfactants were employed. These experimental results indicate that pumice has favorable reservoir characteristics, but, due to its weak brittle nature, it would not be expected that it could withstand the overburden stress at any significant depth. However, it does represent a useful laboratory specimen.

Appendices

Appendix 1: Porosity

Helium Porosimeter

Equations for calculating the effective porosity using a helium porosimeter are as follows:

$$\phi = V_{\text{p}} /V_{\text{b}}$$

(4)

$$V_{\text{b}} = \pi r^{2} L$$

(5)

$$V_{\text{p}} = V_{\text{b}} - V_{\text{g}}$$

(6)

$$V_{\text{REF}} = \frac{{V_{\text{BILLETSREM}} }}{{\left( {\frac{{P_{\text{REFREM}} }}{{P_{\text{CUPREM}} }} - \frac{{P_{\text{REFFULL}} }}{{P_{\text{CUPFULL}} }}} \right)}}$$

(7)

$$V_{\text{g}} = V_{\text{BILLET}} - \left| {\left( {\frac{{P_{\text{REFFULL}} }}{{P_{\text{CUPFULL}} }} - \frac{{P_{\text{REFSAMPLE}} }}{{P_{\text{CUPSAMPLE}} }}} \right)V_{\text{REF}} } \right|$$

(8)

See Tables 10 and 11.

Table 10 Data for calculating the effective porosity of pumice (P) and Tensleep (T) core using a helium porosimeter

Table 11 Data for calculating the effective porosity using the liquid saturation method for pumice and Tensleep

Liquid Saturation

Equations for calculating the effective porosity using the saturation method are as follows:

$$\phi = V_{\text{p}} /V_{\text{b}}$$

(9)

$$V_{\text{b}} = \pi r^{2} L$$

(10)

$$V_{\text{p}} = \frac{{(w_{\text{sat}} - w_{\text{dry}} )}}{{\rho_{\text{brine}} }}$$

(11)

Appendix 2: Data for Grain Size Distribution Analysis

See Table 12.

Table 12 Sieve analysis of pumice and Tensleep