Postanalysis often cannot be applied because of lack of prediction and real-time performance data.Proper postevaluation includes collection of actual job performance data and comparison with predicted cementing performance. A comprehensive cementing simulator is required that accounts for fluid properties, well geometry, changing displacement and mud return rates, and the free-fall effect. Such a simulator has been used successfully in the design of many cementing operations and quite frequently in actual jobs to monitor the progress of the operation. In this paper, case histories are presented to show how this model and on-site measurements can be used for postevaluation of cementing jobs that did not perform as predicted. Two examples illustrate job problems caused by a restriction either in the annulus or in the casing; a third case points out problems associated with use of improperly calibrated pressure gauges during a cementing job.157

Laboratory and field research in Colorado's Wattenberg field showed that commercial gas production was feasible from the very tight Muddy "J" formation using massive hydraulic fracturing. Results indicate that the largest treatments are economically justified in the better areas of the field. Introduction This paper presents the results of a joint research and field effort to develop the very low permeability (0.05 to 0.005 md) Muddy "J" formation in the Wattenberg field by the application of massive hydraulic fracturing (MHF). In this paper, MHF is defined as having a vertical fracture penetration of more than 1,500 ft in each direction from the wellbore. Wattenberg gas production is from the very tight Muddy "J" formation, which is about 50 ft thick and is found at a depth of about 8,000 ft. The bottom-hole temperature in Wattenberg wells is 260 deg. F. Initial attempts to develop the gas potential in this field were made by stimulating wells with 40,000- to 50,000-gal gelled-water fracturing treatments. These efforts resulted in increased gas production; however, the rapid decline of gas production rates with time indicated that the stimulations would be economic failures. Laboratory studies were made to evaluate various fracturing fluids and to investigate fracture flow capacity with various proppant plans. Using these studies, a stimulation program was developed that used a polymer emulsion fracturing fluid and a pillar proppant placement technique. Treatments with up to 500,000 gal of fluid and 1,000,000 lb of sand were conducted. Field case histories are discussed and the results of MHF treatments are compared with those of conventional fracturing treatments. In addition, shut-in temperature logs run before and after treatment, production performance, and mechanical rock properties were evaluated. This information clearly indicates that the largest treatments are economically justified in the better areas of the field, and the fracture penetration is on the order of 3,000 ft. Field Description With an increased demand for gas, better wellhead gas prices, and improved technology, energy companies prices, and improved technology, energy companies are now devoting more attention to the "tight" gas reservoirs heretofore considered noncommercial. The Wattenberg field near Denver is a reservoir that typifies the "tight gas reservoir." Through advancements in fracturing technology, Wattenberg is now considered commercial. The Wattenberg field is located in the western portion of the D-J Basin in Adams and Weld Counties, Colo., and comprises an area of 980 sq miles (627,000 acres) The field was discovered in 1970. During 1974 and 1975 it was under intense development, with approximately 480 gas wells drilled by various companies. Amoco Production Co. is the major operator, with more than 300 Production Co. is the major operator, with more than 300 wells drilled. The Muddy "J" formation of Cretaceous age is the major gas producing zone in Wattenberg. This blankettype sand of extremely low permeability (0.05 to 0.005 md) is found at depths ranging from 7,600 to 8,400 ft (see Table 1 for other pertinent data). The reservoir is stratigraphically controlled by sand pinchout to the southwest and loss in permeability to the northeast. Natural productivity from this very tight formation ranges from a small productivity from this very tight formation ranges from a small show of gas to 100 Mcf/D. JPT P. 10

An experimental program was conducted in the Wattenberg gas field that included borehole measurements, surface measurements, and laboratory tests on oriented cores. Results indicated an apparent variation in azimuth over the field, good correlation between strength anisotropy and fracture azimuth, and that fracture length may not be symmetric around the wellbore. Introduction With better wellhead gas prices and increased demand for gas, it has become economically feasible to produce the so-called "tight" gas reservoirs. Massive hydraulic fracturing (MHF) has proved successful in producing these formations. An MHF stimulation, which may involve thousands of barrels of fluid and 1 million lb or more of proppant material, creates a deep, penetrating fracture proppant material, creates a deep, penetrating fracture extending from the wellbore. These fractures generally proceed along a single azimuth line in both directions proceed along a single azimuth line in both directions from the wellbore and may extend 1 mile or more from tip to tip. The optimum draining of such a reservoir demands a knowledge of the azimuth of the fractures. A field experimental program was set up to measure fracture azimuth in the Wattenberg field. The Wattenberg gas field is located north of Denver, Colo. The Muddy "J" formation is the major gas producing zone. This blanket sandstone formation is found at producing zone. This blanket sandstone formation is found at about 8,000 ft and has permeabilities ranging from 5 to 50 md. Natural gas production from this zone ranges from a small show of gas to 100 Mcf/D. The field can be produced economically only through massive produced economically only through massive fracturing. A more complete description of the field is found in Refs. 1 and 2. The success of massive fracturing in this field indicates that a deep, penetrating fracture is created. History of Fracture Orientation Work This study of the fracture azimuth in Wattenberg field began in 1973, when an attempt was made to monitor the progress of an induced fracture with an arrangement of progress of an induced fracture with an arrangement of seismometers located on the surface. These devices were placed both radially and linearly from the well. However, placed both radially and linearly from the well. However, acquisition systems and processing techniques were unable to discriminate the low-level signals in a relatively high noise environment. A second attempt to determine the direction of fractures was tried in Jan. 1975 at Well G (see Fig. 1), which was completed open hole rather than through casing in Feb. 1971. Wells in Wattenberg normally are completed with 4 1/2-in. casing set through the pay zone, perforated, and fractured. However, Well G was completed open hole and provided an excellent opportunity to try orientation work. Well G, located in the southwest part of the field, was completed originally with an initial flow rate of 791 Mcf/D after stimulation by fracturing with 38,000 gal of gelled water. In Jan. 1975, before restimulation by fracturing with 310,000 gal of polymer emulsion, impression packers were run to determine fracture azimuth. Two attempts were made with 22 ft of packer on tubing. However, both attempts resulted in packer rupture. A third attempt after refracturing was scheduled, but was cancelled because of hole sloughing. Analysis of the first two attempts indicated that hole enlargement caused by the first fracture was the primary cause of failure. JPT P. 185

The results of a joint research and field effort to develop commercial gas production from the very low permeability Muddy "J" Formation in the Watten-berg Field near Denver, Colorado, by the application of MHF (M assive Hydraulic Fracturing) are presented. The Muddy "J" Formation is approximately 50 ft thick and found at a depth of about 8,000 ft. The bottom-hole temperature in these wells is 260'F. Initial attempts to develop the gas potential in this field were made by stimulating wells with 40,000 to 50,000 gal gelled water fracturing treatments. These efforts resulted in increased gas production; however, the rapid decline of gas production rates with time indicated that the stimulations would be economic failures.Laboratory studies were made to evaluate various fracturing fluids and to investigate fracture flow capacity with various proppant plans. Using these studies, a stimulation program was developed which utilized a polymer emulsion fracturing fluid. Treatments with up to 500,000 gal of fluid and 1,000,000 lbs of sand have been conducted.Field case histories are discussed and the results of MHF treatments are compared with the conventional frac-turing t reatments. It was found that the well and treatment payout time was inversely proportional to the treatment size in the better areas of the field showing that the larger treatments are more desirable than the smaller ones.In the poorest areas of the field, well and treatment payout is indefinite at the current inter-state gas price. INTRODUCTION With an increased demand for gas, better well-head gas price and improved technology, the energy companies are now devoting more attention to the "tight" gas reservoirs heretofore considered non-commercial. Amoco is one such company, and the Wattenberg Field of Colorado is a reservoir which typifies the "tight gas reservoir". Through advance-ments in fracturing technology, Wattenberg is now considered commercial.The Wattenberg Field is located in the western portion of the D-J Basin in Adams and Weld Counties, Colorado, and comprises an area of 980 square miles (627,000 acres). The field was discovered in

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