Successful Stimulation of Deep Wells Using High Proppant Concentrations
S. A. Holditch, SPE-AIME, ShellOilCo. Services John Ely, SPE-AIME, Halliburton
Large portions of the easily recovered hydrocarbons of the world are rapidly being depleted. This is particularly the case in the confines of the western hemisphere where many of the most productive fields are inthe latter stages of primary and secondary recovery. If complete dependence on foreign oil or a large energy gap is to be averted, new supplies of energy must be found soon. One promising source is the oil and gas tightly held in formations that have very low permeability and porosity. If these formations, a large number of which are deep, high-temperature reservoirs, are to be economicallyproduced, an effective means of stimulation must be developed. tests were apparently successful in safely setting off a nuclear device and achieving some stimulation, However, the economic feasibility of nuclear stimulation is still questioned by a large segment of the industry. The use of conventional explosives presents a considerable hazard during injection; detonation in thin layers at largedistances from the wellbore is difficult and not always successful. The third type of stimulation is hydraulic fracturing. Since the inception of fracturing in 1949, many different fluids and proppants have been investigated.’-’ In the early 1950’s, viscous petroleum base fluids were being used industrywide. From the mid1950’s through the mid-1960’s, the trend was to use less viscous fluids pumped athigher rates. Also, the trend has been toward using water-based fluids rather than oil-based fluids for fracturing, The theory of fracturing developed quite rapidly between the mid-50’s and mid-60’s. In 1957, Howard and Fastg introduced some of the first literature for the calculation of fracture geometry from treatment data. Since that time a continuous stream of literature, which is much tooabundant to reference completely, has been published on fracture dimensions and design criteria. The work that has been published indicates that the ratio of (1) fracture length to the radius drained, and (2) fracture flow capacity to formation permeability are the most critical relationships in the design.’” The methods most often used for predicting productivity increase are those by McGu~re and$kora,’1 by Prats,’2 and k
Types of Stimulation
There are basically three different types of stimulation methods available to the industry today. The first, chemical stimulation, has not been useful in tight sandstone reservoirs except in the removal of formation damage,1 In deep, high-temperature and highly soluble formations, it is difficult to use this technique because the acid is ra~i~lyspent near the wellbore, Without deep penetration of live acid into the fracture, effective stimulation ca:~ be achieved. not In some cases the use of large volumes of fluid to cool the formation helps to overcome this deficiency, The second type of stimulation, which is undergoing limited study today, is the use of both conventional and nuclear explosives.2-4At this time, two nuc!ear explosiveprojects have been conducted, The
A unique viscous fluid has been used in fracturing deep, high-temperature reservoirs. By using large treatments and high concentrations of proppants, reservoirs with low permeability and porosity can be successfully stimulated. Data from widely varying formations are compared, with special emphasis on the Vicksburg.
Tinsley et al.” Allof these predict production increase ratios as functions of fracture conductivity and fracture penetration. It is apparent, upon review of the information relating the variables*O-lsto be considered, that for tighter rocks it is desirable to have a longer fracture with moderate flow capacity. However, obtaining even moderate flow capacity in the deeper formations has always presented problems,...