Field Validation of Acidizing Wormhole Models

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn matrix acidizing of carbonate reservoirs, the generation of wormholes is a major key to success. Numerous papers have been written that describe the formation and propagation of such wormholes. Generally, these models have been based on sound chemistry and physics. Some of the models have been validated against laboratory experiments that are generally conducted in a linear geometry. However, in order to use the models in the design of matrix acid stimulation treatments, the models need to be validated under radial flow conditions that dominate field treatments.Radial flow, competing wormholes, permeability contrasts, and reservoir height are example parameters that cannot easily be validated in laboratory experiments. Scaling of the models to field conditions might be required. Two types of models have been written for aiding in treatment designs. One model, called a linear-type model, is fully consistent with the decades of linear flow tests conducted in the laboratory. The second model, called a symmetry model, is exceedingly difficult to validate in the laboratory. This paper evaluates both models against treating pressure responses from field treatments.A matrix treatment simulator was used that includes such effects as multiple formation layers with independent formation parameters and allows for modeling zonal coverage. The formation parameters include permeability, porosity, mineralogy, acid reactivity, skin damage, and permeability contrast. The well parameters include height of the layers, wellbore tubulars, friction pressures, etc. This simulator was an ideal framework for evaluating the two acidizing wormhole models. This paper demonstrates the key issues related to the interaction between the wormhole models and zonal coverage.

An Acid-Placement Model for Long Horizontal Wells in Carbonate Reservoirs

“…The PV bt can vary from as low as one, or even slightly lower, when acid is injected at near the optimal rate in limestone, to as high as 50 when the wormholing process is not efficient. We also note that the wormholing model presented by Gdanski 2,7,8 , which is presented by Glasbergen et al 8 as…”

Improved Acid Diversion Design Using a Placement Simulator

“…This confidence is not only based on the evaluation of the field cases describe in this paper and in previous papers. 12,13 . The model has also been used successfully in the design and evaluation of many acid treatments in a large variation of reservoirs worldwide over the last couple of years.…”

“…Another approach that has been used in the past and has been applied to the model discussed in this paper in previous publications 12,13 is to obtain a pressure match versus time between simulator predicted and actual treatment pressures. Treating pressures are preferably measured using a bottomhole pressure gauge to eliminate uncertainties associated with the prediction of tubing friction pressures.…”

Improved Acid Diversion Design Using a Placement Simulator (Russian)

“…Применение этого подхода к данной модели было рассмотрено в работах, опубликованных ранее. 12,13 Давление закачки желательно измерять с помощью забойного манометра, чтобы избежать неопределенностей, связанных с прогнозированием потерь давления на трение в НКТ. Сравнение расчетного и измеренного давления обработки также является хорошим показателем.…”