The two most promising techniques for producing natural gas from hydrate reservoirs are depressurization and brine injection. This paper examines the dissociation characteristics of methane hydrates during these processes. A correlation for the rate of hydrate dissociation during brine injection as a function of salinity, brine temperature, brine injection rate, pressure, and hydratelbrine surface area is presented. Depressurization experiments show that hydrate dissociation results in a decrease in the rate of pressure decline and contributes significantly (15% to 70%) to the cumulative gas production.

This paper presents a technique to forecast the production from horizontal wells in rectangular drainage areas. The technique is useful for wells located either centrally or offcentrally in the areal drainage plane. Analytical pressure transient solutions were used to calculate the shape factor, CA, and the corresponding equivalent skin factor, sCA. Moreover, dimensionless time at which the pseudo-steady state begins is reported for centered and off-centered horizontal wells and fully penetrating infinite-conductivity vertical fractures. These results are presented in the form of easy to use correlations. Furthermore, these correlations were tested by analyzing the relevant pressure transient data reported in the literature. The pseudo-steady state shape factor, CA, and skin term, sCA, for a horizontal well approaches fully penetrating infinite-conductivity vertical fracture for very large values of dimensionless horizontal well length, LD. Knowledge of shape factor, CA, and of corresponding beginning of pseudo-steady state time, tDA, pss would facilitate computation of the horizontal well production forecast from a corresponding infinite-conductivity, fully penetrating vertical fracture forecast. The methods for prediction of the inflow performance relationship for horizontal wells is also outlined, using example problems representative of horizontal well applications in on-shore and off-shore areas. Introduction In recent years, horizontal wells have been increasingly used in field applications. Currently, various commercial techniques are available to drill, complete and test horizontal wells. The up-to-date technology of drilling, completion, testing, as well as production forecasting for horizontal wells and related vertical well technology has been reviewed by various authors. A horizontal well pressure analysis has shown that the horizontal well behaves as a vertical fracture with a fracture height equal to the wellbore diameter. The insignificant pressure drop observed in the horizontal wells indicates an infinite-conductivity for the flow in the wellbore. On the other hand, it is difficult to obtain infinite fracture conductivity in a conventional fracture stimulation. Thus, horizontal wells would provide an alternative for conventional fracture stimulation. The state of the art review of the reservoir engineering aspects of horizontal well production has been presented by Giger et al. and others. The pressure transient solutions for horizontal wells in finite and infinite reservoirs have been discussed by various authors in the literature. However, there seems to be a lack of information regarding the influence of the drainage area and its shape on horizontal well performance. The purpose of this paper is to address this issue. The shape factors indicate the influence on well productivity of well location within the drainage boundary.

Since 2005, Williams Production Gulf Coast Company has drilled over 100 horizontal wells in the Barnett Shale. The Barnett Shale is an unconventional gas reservoir that encompasses a nineteen county area in the Fort Worth Basin. Slick-water fracturing is the primary technique that has been used to hydraulically fracture the wells. Recently, Williams as well as several operators have tried fracturing two or more adjacent wells simultaneously with the goal of exposing the shale to more pressure and produce a more complex web of fractures, thereby improving the initial rates and reserves. Simultaneous fracturing or simo-frac technique is expensive and requires much more planning, coordination and logistics as well as a larger surface location. In this paper, the case history of sequential and simultaneous fracturing of four similarly drilled and completed horizontal azimuth wells in Eastern Parker County, is discussed. All the four wells where stimulated with near identical fracture treatments. The sequentially/simultaneously fractured wells resulted in IPs of 3.3 MMscfd to 3.5 MMscfd with 30-day averages ranging from 2.1 MMscfd to 2.9 MMscfd. The 4th well was a single offset horizontal well drilled with effective lateral 2400 ft less than a quarter mile to the north but had significantly lower IP of 2.3 MMscfd and 30-day average production of 1.2 MMscfd. The initial comparative test results are very encouraging and indicate a more complex fracture network being created in the vicinity of the sequentially/simultaneously fractured wells, which results in a significantly improved well performance. Williams continues to evaluate the benefit of simultaneous fracturing and has done more simo-frac jobs in other counties with good results. As in this case history, due to surface and lease constraints, many of the simo-frac jobs are being done in wells that are drilled from the same dual pad and have well spacing of the order of 500 ft to 700 ft. The paper also provides an analysis of the simultaneous fracturing jobs done to date in Parker and Johnson County. Background The Barnett Shale has evolved into the pre-eminent shale-gas resource plays in the US and is now considered by many as the largest onshore natural gas field in the United States. The productive part of the formation is estimated to stretch an area covering 5000 square miles, encompassing 19 counties (Figure 1). According to the latest figures from the Texas Railroad Commision published in June 2008, there are more than 7700 producing wells and 185 active operators in the Barnett Shale with permits for more than 4,500 additional wells. Production from Barnett Shale currently exceeds 3.7 Bcf/d, accounting for more than 15% of Texas gas production, and more than 3.8 Tcf of gas has been produced from the Barnett Shale since 20001. Simultaneous fracturing (simo-fracs) of paired offset wells is one of the recent trends in Barnett fracturing and is being increasingly used by many operators. In this technique, two or more adjacent wells that are roughly parallel to each other, are fractured simultaneously. The goal is to expose the shale to more pressure and produce a more complex, "three-dimensional web" of fractures by increasing the density of the hydraulic fracture network and increasing the surface area created by the frac job. The drainage area of each of the wells is enhanced as the frac fluid is pushed into the space between the two wells that would not have been fractured if the operator had drilled only well2–3.

Since 2001, Williams Production Mid-Continent Company has drilled over 200 horizontal wells in the Hartshorne Coal in the Arkoma Basin in southeastern Oklahoma. The Arkoma basin is an elongate sedimentary basin extending from east-central Oklahoma into Arkansas (Figure 1). The primary zones producing CBM gas in the Arkoma Basin are the Hartshorne sand, and, the Upper Hartshorne Coals, which coalesce into one bed towards the north, and, are the most actively explored gas producing reservoir in the western Arkoma basin. The Hartshorne Coal is a member of the Pennsylvanian Hartshorne Formation, which is a part of the Krebs Group of the Desmoinesian Series (Figure 2). The coals range from high-volatile bituminous to low-volatile bituminous in rank. The Hartshorne Coal encompasses a large area in Haskell, Pittsburg, LeFlore, and, McIntosh counties, and, ranges from 3 ft to 7 ft in thickness. Typical average horizontal drilled length has ranged from 2000 ft to 2500 ft, with the longest well being over 3000 ft. The wells are usually completed with a slotted liner. Unlike CBM wells in other areas of the United States, Hartshorne coal wells are relatively "dry", and, typically produce gas from the first month, with very little water production. This paper presents examples of using analytical techniques for production forecasting, and, reserves estimation for horizontal CBM wells in the Arkoma basin. The production analysis results were integrated with core data, and, material balance calculations, and, indicate recovery factors ranging from 50% to 80% for the Hartshorne CBM wells. The paper also provides a comparison of the performance of horizontal and vertical CBM wells in the basin. In addition, pressure buildup tests were conducted on over 40 horizontal wells, to estimate the reservoir pressure, and, to calculate permeability and skin factor. The paper presents two examples of pressure buildup analysis for Arkoma horizontal CBM wells. The PBU analysis indicated effective permeability in coal of the order of 30 md, which is attributed due to the significant cleating of the Hartshorne coal in the area. The paper includes guidelines for drilling horizontal wells for exploitation of Hartshorne CBM. 1. Introduction CBM activity in the US has been growing steadily nearly every year since 1989. According to the US department of energy, the contiguous United States is estimated to have CBNG in-place resources of 700 trillion cubic feet (Tcf), of which 100 Tcf may be economically recoverable1. In Oklahoma, in the last decade alone, over 3000 CBM wells have been drilled, primarily in the Arkoma and the Cherokee basins. The CBM production in Oklahoma has been growing at an exponential rate for the last several years, and, the cumulative gas production through 2005 was 154 Bcf 2. In general, the Hartshorne coal in the Arkoma are thicker and deeper than those in the northeast Oklahoma shelf. Statistically, they also have higher initial producing rates and significantly lower water production. The low water producing rates is one of the main things that makes the Hartshorne coal unique from most coals in the U.S. Even in the horizontal completions where significantly more pay is exposed, the average water producing rate is 10 barrels of water per day. There is obviously no "dewatering period" with Hartshorne coals that a lot of other coals exhibit.