Improved Stimulation Of The Escondido Sandstone
Authors: Kundert D.P. , Smink D.E. 
Published: December 2007

This paper presents the results of an effort to improve productivity of the low permeability Escondido Formation in Webb County, Texas by the use of an improved hydraulic fracture design.

A fracture treatment using the polymer emulsion fluid system was designed to provide sufficient propped fracture length and area to maintain long term productivity of the wells. The polymer emulsion fluid was selected for its good proppant transport and low fluid loss properties. properties. Five previously drilled and stimulated wells and three new wells were fractured with the polymer emulsion treatments. Evaluation of pre and post frac flow rates and decline curves indicates an approximate doubling of recoverable reserves.

Introduction

The Mesquite Field is in Webb County in Southwestern Texas about 15 miles north of the town of Laredo. Drilling was started in the mid 1970's. The Escondido production occurs within a broad stratigraphic trap. Production from the wells on initial Production from the wells on initial completion without stimulation is considered non-commercial. The Escondido is recognized to have significant potential for producing natural gas.

The wells in the Mesquite Field are located on approximately a 320 acre (127.5 hectare) spacing. However, well performance indicates that 160 acre (64.75 hectare) spacing may be more suitable for estimating reserves. Based on the 160 acre (64.75 hectare) spacing the wells contain an average estimated gas in place quantity of 1500 mmcf (4.25 E+07 m3).

It is evident that even though a good amount of gas is present, the production rate needs to be improved to make the wells commercial. Previous attempts to increase production by "conventional" gelled water fracs production by "conventional" gelled water fracs were partially successful, but rapid declines in production indicated that an improved stimulation treatment was necessary to maintain long tern productivity.

EARLY STIMULATIONS

Recognizing that stimulation was necessary, the first five wells were fractured using approximately 40,000 gallons (151.4 m3) of gelled water containing an average of 80,000 pounds (36,280 kg) of 29–40 mesh frac sand. pounds (36,280 kg) of 29–40 mesh frac sand. This is a low viscosity (30 to 40 centipoise) gelled water system. The jobs were pumped down casing at 25–30 barrels per minute (4–5 m3/min).

Initial results of these treatments indicated an improvement in production of about 2 fold, but after only 2 to 3 months the wells had declined to the pre-frac flow rate.

Part of the problem with these treatments could possibly be a result of the proppant bed deposited in the fracture. Due to the low viscosity of the fracturing fluid it is possible that the propping sand settled rapidly, possible that the propping sand settled rapidly, leaving a short frac with a low bed height. This could result in only the bottom few feet of the zone of interest actually being propped with a conductive fracture.

FORMATION EVALUATION

The Escondido is a tight gas Sandstone of Cretaceous age. The sand was deposited in a lagoonal environment and is comprised of fine quartz, silt, clay, and carbonate cement.

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