Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. A log-log plot that is very useful in predicting when the fracture is in tip-screen-out mode and whether the fracture is being widened or height growth is occurring.
Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. A fracture treatment, common where high fracture flow conductivity is needed. Very high pressures and very high proppant loadings are applied near the end of a fracture treatment where the tip of the fracture has stopped growing due to bridging of proppant at the fracture dip because of dehydration (frac fluid leakoff).
Tight gas is the term commonly used to refer to low permeability reservoirs that produce mainly dry natural gas. Many of the low permeability reservoirs that have been developed in the past are sandstone, but significant quantities of gas are also produced from low permeability carbonates, shales, and coal seams. Production of gas from coal seams is covered in a separate chapter in this handbook. In this chapter, production of gas from tight sandstones is the predominant theme. However, much of the same technology applies to tight carbonate and to gas shale reservoirs. Tight gas reservoirs have one thing in common--a vertical well drilled and completed in the tight gas reservoir must be successfully stimulated to produce at commercial gas flow rates and produce commercial gas volumes. Normally, a large hydraulic fracture treatment is required to produce gas economically.
In addition to knowing the values of in-situ stress, it is also extremely important to know the values of formation permeability in every rock layer. In addition, one must know the formation permeability to forecast gas reserves and to analyze post-fracture pressure buildup tests. To determine the values of formation permeability, one can use data from logs, cores, production tests, and prefracture pressure buildup tests or injection falloff tests. The most data that are available vs. depth comes from openhole logs. If the logs are analyzed correctly, it is often possible to generate estimates of formation permeability vs. depth using the logging data.
Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. Characteristic markings (ridges, tears, risers, etc.) on fracture surfaces after fatigue crack of fracture propagation (also known as clamshell marks, conchoidal marks and arrest marks).