Matrix Treatment Employs New Acid System for Stimulation and Control of Fines Migration in Sandstone Formations

Abstract

Summary A matrix acidizing system employing fluoboric acid (HBF4) has been developed to stimulate problem sandstone formations. The fluoboric acid hydrolyzes to generate hydrofluoric acid (HF), thus achieving deeper live-acid penetration. Laboratory tests also show that spent fluoboric acid reacts with undissolved clay to reduce cation exchange capacity greatly and render the clay insensitive to incompatible fluids. Introduction Sandstone matrix acidizing long has been used as a means of improving production of oil. and gas by removing formation damage and increasing permeability of the zone immediately around the wellbore. Laboratory and field studies1–4 have demonstrated the effectiveness of this type of treatment. In spite of widespread use, however, many formations do not respond satisfactorily to conventional HCl/HF treatments. This normally is attributed to rapid spending of HF near the wellbore. Some wells initially show good stimulation but later experience an unusually rapid decline in production rate. Such production declines commonly are observed in wells producing from both consolidated and unconsolidated sands. The declines usually are attributed to plugging by migratory clays and other fines. Formation plugging by migratory fines was demonstrated by Krueger et al.5 in both laboratory and field studies. Core test results revealed that high flow rates caused dislodgment of fines with resulting loss of permeability. Krueger also reported field studies in which the production decline rate was accelerated by flowing wells above an optimal rate. As the production rate was increased, a corresponding increase in inorganic solids content of the produced oil also was observed. These observations strongly support the theory of formation damage from fines migration. Migratory fines apparently are released first by exposure to strong acid and later by mechanical forces resulting from the increased flow of produced fluids. Various treatments and production techniques6 have been devised in an effort to control or minimize this problem. Krueger et al.5 and Templeton et al.7 described treating techniques in which wells, following stimulation, were returned to production at a gradually increasing rate to minimize fines migration. Various clay stabilizing agents8,9 also have been applied in an effort to control movement of fines. Also, delayed acting acidizing systems7,10 have been developed to provide deeper live-acid penetration and, thus, remove damaging fines some distance from the wellbore.

A Method for Assessing the Impact of Secondary and Tertiary Reactions on Sandstone Acidizing Treatments

“…However, placing a small amount of stabilizing borosilicate is desired to prevent future fines migration damage around the wellbore. Because of the presence of boron in the clay-stabilizing acid, the borosilicate precipitated from secondary and tertiary reactions tends to fuse the migratory clays to the pore walls [25][26][27]. Figure 7 shows the volume and the location of borosilicate precipitated in the reservoir for different volumes of the clay-stabilizing acid.…”

“…Fluoboric acid is more retarded than mud acid and therefore permeability improvement is realized much deeper in the reservoir (Figs 11a and 11b). Fluoboric acid controls fines migration problems by precipitation of a non-damaging layer of borosilicates [25][26][27]. Figures 11e and 11f show that a borosilicate layer has been effectively precipitated near the wellbore in both zones.…”

Uso de nanopartículas de sílice para la estabilización de finos en lechos empacados de arena Ottawa

“…Cuando la energía de interacción total entre la partícula y la superficie porosa se vuelve positiva, las fuerzas repulsivas son más grandes que las fuerzas atractivas, y se desprenden los finos Thomas and Crowe, 1981).…”

Mathematical modelling of formation heat treatment process

“…Measures to stabilize clay swelling and migration have been discussed in the literature (Himes et al, 1991;Borchardt et al, 1984;Theng, 1984;Reed, 1974;Coppell et al, 1973;Plummer, 1991). Curative methods have also been attempted and presented in the literature (Hayatdavoudi et al, 1992;Lund et al, 1976;Thomas and *Author to whom correspondence should be addressed. Present address: Hycal Energy Research Laboratories Ltd., 1338A -36th Avenue N.E., Calgary, Alberta, Canada T2E 6T6.…”

“…Present address: Hycal Energy Research Laboratories Ltd., 1338A -36th Avenue N.E., Calgary, Alberta, Canada T2E 6T6. Crowe, 1981;Garst, 1957;Sloat, 1989;Schaible, 1986;Crowe, 1986). The two most popular non-thermal stimulation processes are hydraulic fracturing and matrix acidizing.…”