Abstract

This paper describes an innovative fracture treatment design approach that has been successfully used to improve the productivity of Fruitland coal CBM completions. The process integrates real-time treating pressure evaluation to adjust key treatment parameters on the fly and maintain a low net pressure development. The low net pressure development indicates good proppant distribution through the created fracture geometry and minimizes potential formation/fracture damage from the fracturing fluids. This results in shorter de-watering periods and accelerates peak production of the Fruitland Coal completions.

In the Fruitland Coal, the dominant fracturing mechanism controlling the ability to distribute proppant laterally into the far-field is the quality of the near-wellbore connection. Complex near-wellbore fracture geometries result in a convoluted slurry pathway, which hinders lateral proppant distribution into the far-field. Further, if the near-wellbore connection was not mitigated effectively, the overall net pressure development while placing proppant became excessive. This paper discusses the innovative changes made to improve the near-wellbore connection, allowing the treatment to be completed and productivity of the well increased.

Based on an offset well study, it was observed that excess net pressure development damaged the fracture conductivity and/or the cleat system of the coal. When an excessive level of net pressure was developed, polymer dehydration into the cleat system caused irreparable damage to the existing permeability. Evidence of the damage was indicated by the extended load fluid recovery time. Since de-watering of the coal begins only after the load is recovered, it was observed that gas production was significantly delayed when the net pressure development during the propped fracture treatment was excessively high.

Observing this relationship, treatment designs were altered, but more importantly, real-time assessment of the treatment pressure character was found to be essential in achieving design objectives. The completion approach discussed in this paper has been employed in over thirty-five Fruitland Coals completions over the past three years with excellent production results.

Introduction

The Fruitland Coal produces gas from coal seams across the San Juan Basin. The San Juan Basin, located in SW Colorado and NW New Mexico, is a gas producing basin with several productive horizons in addition to the Fruitland Coal. (See Figure 1, Area Map). The Pictured Cliffs formation, a blanket sandstone, produces gas just beneath the Fruitland Coal. Some wells in the area commingle the Pictured Cliffs (PC) sands with the Fruitland Coal after hydraulic fracturing both zones either separately or combined. The PC sands have significantly higher permeability than the Fruitland Coal systems and as a result are generally depleted throughout the San Juan Basin.

The Fruitland Coal is usually completed with 4 1/2" casing and 2 3/8" tubing. The wells are de-watered using rod pumps and then once gas production begins, the wells are allowed to flow up the tubing/casing annulus. Compression is used to lower the surface flowing pressure to approximately 25 psi.

The Fruitland Coal typically consists of a primary bench having a thickness ranging from 15 to 25 feet. Usually there are two to five additional coal stringers up hole that may vary from 2 to 6 feet thick. The depth of the Fruitland Coal benches in the study area ranged from 1,500 feet to 2,000 feet MD. After the wells are cased, the Fruitland Coal benches are perforated and hydraulic fracture stimulated.