Study of The Field Application of Sandstone Acidizing (includes associated papers 6507 and 6555 )
Authors: Gidley J.L. , Ryan J.C. , Mayhill T.D. 
Published: December 2007

In a study to determine what factors most influence sandstone acidizing andproduction response infield treatments, it was found that the mostcritical factors are mud-acid volume and treating pressure. The optimumresponse was obtained with mud-acid volumes of 125 to 200 gal/ft; the poorest treatment response occurred when acid was injectedat pressures in excess of fracturing pressure.

Introduction

Much of the improvement in stimulation proceduresduring recent years has come about as a result of closelyexamining field experience. Exxon Co., U.S.A., periodically examines the success of stimulation treatments as afunction of treatment design parameters and reservoircharacteristics. Such an examination was made recentlyconcerning experience gained from April through Sept.1973. Although the original survey covered acidizing, fracturing, and surfactant methods of well stimulationand involved the treatment of both sandstone andcarbonate formations, this paper describes only the resultsfound for sandstone acidizing. As the study developed, more data were examined than were available during the6-month survey period cited. In some cases, field resultsfrom Jan. 1968 through May 1974 were examined. Overall, 222 treatments from the Texas-Louisiana Gulf Coast, West Coast, and Mid-Continent areas were examined.Test data from the Mid-Continent area were too few tojustify a separate analysis. The most detailed data wereavailable for treatments along the Texas Gulf Coast -an area where the acid-mutual solvent method isextensively used. Success of sandstone acidizing was related tothe design and execution parameters of the treatment andto reservoir characteristics thought to be significant.

The outcome of a treatment was judged first on apurely economic basis. A treatment was called successfulif the increase in oil production provided payout of the jobcosts within a 3-month period. This payout was based onpre-embargo oil prices and involved an oil value of$2.20/bbl after federal income tax. This criterion is morestringent than current economic conditions wouldwarrant, and some jobs ruled unsuccessful in this studywould be ruled successful if re-evaluated.

The data gathered on each job in the study are shown inTable 1. The factors of most interest were the size andcomposition of each of the three phases of a standardacid-mutual solvent treatment, the manner of executionof the treatment in the field, and several reservoirparameters. The last category comprised the porosity andpermeability of the formation, the length of theperforated interval, and the depth, bottom-hole pressure, andtemperature of the formation. No effort was made toperform a detailed mineralogical analysis of theformations treated because of the time and expense involved.Manipulation of the data acquired was accomplished by aMark IV computer program.

The range of the study and the names of the formationstreated are shown in Table 2. A wide range of geologicages and a broad spectrum of formation depths, temperatures, porosities, and permeabilities were considered. Depth ranged from 1,010 to 13,358 ft, formationtemperature from 95 degrees to 275 degrees F, porosity fromless than 7 to 36 percent, and formation permeabilityfrom 1 to 2,350 md.

JPT

P. 1289^