Program Gas Well Build-Up Testsa Field Case Illustration Of Solution Through The Use Of Combined Techniques
Authors: Wasson J. , Mattar L. 
Published: March 2010

This paper illustrates with a four-well example several problems that can be encountered ill the analysis of pressure buildup data.

The subject wells being analyzed are in the Ghost River (Salter) Field in southern Alberta, Canada. They are completed in either single or dual zone low permeability Mississippian carbonate sour gas reservoirs, and in all cases have been given acid fracture stimulations. Of the seven tests analyzed, only one test had complete bottomhole pressure data available. Of the remainder, two had partial bottomhole recorded pressure data and four had only surface-recorded pressure data. Other important points to the evaluation are:—hydrates were encountered throughout much of the testing; as a result, production test flow rates varied considerably in some cases—commingling of production from two zones occurred in some of the tests—changing wellbore temperature effects are evident—only minor amounts of reservoir liquids were produced during testing.

Through the combined use of pseudo-pressures, superposition radial flow plots, square root plots, type curves, wellbore storage theory and other techniques, solutions are obtained and interpretations made.

FIGURE 1. Field and well location map, Ghost River (Salter). (Available in full paper)

Introduction

The Ghost River Field (also named the Salter Field by the Alberta Energy Resources Conservation Board) lies in the Alberta Foothills approximately 40 miles west northwest of the city of Calgary, as shown in Figure 1. The field is defined by four gas wells (in Lsd's 4–1–27–8, 4–36–26–8, 6–25–26–8, and 15–24–26–8 W5M), one suspended well, and two dry holes.

Three of the subject gas wells (4–36, 6–25, and 15–24) were completed in two zones, being the Mount Head and Turner Valley Sections of the Mississippian Formation. The remaining gas well (4–1) was completed in only the Mount Head Section. A typical well completion is illustrated in Figure 2. Net pays vary from 25 feet in the Mount Head at 4–1 to a total of 243 feet in the two zones at 6–25. Average porosity in each zone is approximately 4%. Wellbore and reservoir parameters for the Ghost Field are listed in Table 1.

All wells were acid stimulation fractured. Following the fracturing, production tests with varying rates and test procedures were run.

On the discovery well, 4–36–26–8 W5, each zone was completed, fractured and AOF tested separately. However, downhole hydrate formation hampered the individual zone AOF tests. Finally, a commingled Mount Head and Turner Valley test was run in order to get a rate high enough to overcome the hydrate problems.

As a result of the difficulties experienced with 4–36, the test procedures on subsequent wells were modified. The Mount Head and Turner Valley zones were commingled from the start, less clean-up flow was used, and more emphasis was placed on obtaining build-up data. Typical early and later flow test procedures are illustrated in Figures 3 and 4, respectively.

TABLE 1, Ghost River Field — reservoir data (Available in full paper)

A study was undertaken to analyze these tests, with the major objective being to determine values of the reservoir permeability.