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Liang, Tianbo (China University of Petroleum, Beijing) | Xu, Ke (Massachusetts Institute of Technology) | Lu, Jun (University of Tulsa) | Nguyen, Quoc (University of Texas at Austin) | DiCarlo, David (University of Texas at Austin)
Summary Hydraulic fracturing can create a large fracture network that makes hydrocarbon production from low-permeability reservoirs economical. However, water can invade the rock matrix adjacent to the created fractures and generate water blockage that impairs production. Using surfactants as fracturing-fluid additives is a promising method to enhance the fluid flowback, and thus mitigate the water blockage caused by invasion. It is imperative to understand how surfactants work during the fracturing and production stages, so as to maximize their effectiveness in production enhancement. In this study, an experimental investigation is conducted using a "chipflood" sequence that simulates fluid invasion, flowback, and hydrocarbon production from hydraulically fractured reservoirs. All experiments are conducted in a 2.5D glass micromodel that provides direct observation of in-situ phase changes when different Winsor types of microemulsions formed in the porous medium. The results provide direct evidence of the impact of the matrix-fracture interaction as well as water removal when surfactants are used. They further elucidate why surfactants under different Winsor-type conditions perform differently in mitigating the water blockage. This helps to clarify the screening criteria for optimizing flowback surfactant in hydraulic fracturing. Introduction Hydraulic fracturing increases the contact area with the formation, thus making hydrocarbon production from low-permeability reservoirs economical. During the hydraulic-fracturing job, a massive amount of water is pumped into the formation to create the fracture network; however, only 5-50% of water can flow back before and during the production stage (King 2012; Wasylishen and Fulton 2012; Cao et al. 2017; Xu et al. 2017c). Although a fraction of water is retained within the wellbore, in the bottom of vertical fractures (Agrawal and Sharma 2013), and in the closed "induced unpropped fractures" (Sharma and Manchanda 2015), well productivity is mainly affected by the water invading the formation adjacent to the created fractures. It has been experimentally observed that water imbibition can be pronounced even in tight and ultratight rocks with permeability ranging from hundreds of nanodarcies to tens of microdarcies (Pagels et al. 2013; Bostrom et al. 2014; Dutta et al. 2014; Engelder et al. 2014; Lan et al. 2014). Since the estimated ultimate oil-recovery rate in low-permeability reservoirs is likely less than 10% (EIA 2015; Wachtmeister et al. 2017; Hu et al. 2018) and the production is mainly attributed to the formation adjacent to the propped fractures (Patzek et al. 2014; Yu and Sepehrnoori 2014; Male et al. 2016; Zuo et al. 2016), the invading water, even if not deep into the formation, can hinder hydrocarbon flow from the formation to the fractures.
Dong, Pengfei (Rice University) | Puerto, Maura (Rice University) | Jian, Guoqing (Rice University) | Ma, Kun (Total) | Mateen, Khalid (Total) | Ren, Guangwei (Total) | Bourdarot, Gilles (Total) | Morel, Danielle (Total) | Biswal, Sibani Lisa (Rice University) | Hirasaki, George (Rice University)
Summary The high formation heterogeneity in naturally fractured limestone reservoirs requires mobility control agents to improve sweep efficiency and boost oil recovery. However, typical mobility control agents, such as polymers and gels, are impractical in tight sub‐10‐md formations due to potential plugging issues. The objective of this study is to demonstrate the feasibility of a low‐interfacial‐tension (low‐IFT) foam process in fractured low‐permeability limestone reservoirs and to investigate relevant geochemical interactions. The low‐IFT foam process was investigated through coreflood experiments in homogeneous and fractured oil‐wet cores with sub‐10‐md matrix permeability. The performance of a low‐IFT foaming formulation and a well‐known standard foamer [alpha olefin sulfonate (AOS) C14‐16] were compared in terms of the efficiency of oil recovery. The effluent ionic concentrations were measured to understand how the geochemical properties of limestone influenced the low‐IFT foam process. Aqueous stability and phase behavior tests with crushed core materials and brines containing various divalent ion concentrations were conducted to interpret the observations in the coreflood experiments. Low‐IFT foam process can achieve significant incremental oil recovery in fractured oil‐wet limestone reservoirs with sub‐10‐md matrix permeability. Low‐IFT foam flooding in a fractured oil‐wet limestone core with 5‐md matrix permeability achieved 64% incremental oil recovery compared to waterflooding. In this process, because of the significantly lower capillary entry pressure for surfactant solution compared to gas, the foam primarily diverted surfactant solution from the fracture into the matrix. This selective diversion effect resulted in surfactant or weak foam flooding in the tight matrix and hence improved the invading fluid flow in the matrix. Meanwhile, the low‐IFT property of the foaming formulation mobilized the remaining oil in the matrix. This oil mobilization effect of the low‐IFT formulation achieved lower remaining oil saturation in the swept zones compared with the formulation lacking low‐IFT property with oil. The limestone geochemical instability caused additional challenges for the low‐IFT foam process in limestone reservoirs compared to dolomite reservoirs. The reactions of calcite with injected fluids—such as mineral dissolution and the exchange of calcium and magnesium—were found to increase the Ca concentration in the produced fluids. Because the low‐IFT foam process is sensitive to brine salinity, the additional Ca may cause potential surfactant precipitation and unfavorable over‐optimum conditions. It, therefore, may cause injectivity and phase‐trapping issues especially in the homogeneous limestone. Results in this work demonstrated that despite the challenges associated with limestone dissolution, the low‐IFT foam process can remarkably extend chemical enhanced oil recovery (EOR) in fractured oil‐wet tight reservoirs with matrix permeability as low as 5 md.
The existence of petroleum in California has been known for many years. Fromtime immemorial the California Indians used this mineral, in the form ofasphaltum, for various purposes. In the early history of the State the Catholicfathers utilized it for the roofing their missions and other buildings. It is said that in 1855 or 1856 Andreas Pico distilled petroleum on a smallscale for the San Fernando Mission. He obtained his crude oil from Pico canon, near Newhall, in Los Angeles county; and he was probably the first refiner of petroleum in this State. In 1856 a company commenced work at the La Brea ranch, in Los Angeles county, and tried to refine the crude oil. In 1857 an attemptwas made to produce illuminating-oil from crude petroleum at Carpentaria, inSanta Barbara county; and there are records of similar attempts in otherlocalities previous to 1860; but none of them were successful. The first scientific report on petroleum in California was made by Prof. B.Silliman, who published his researches in 1865. He spoke favorably of thepossibility of obtaining petroleum in remunerative quantities in this State, and gave the results of his experiments in the Fractional distillation ofCalifornia petroleum. The next decade was marked by a considerable oil-excitement in California; anda great many companies were formed for the purpose of petroleum-mining and fordistilling crude oil. In most instances these companies did not meet with success; but it must beremembered that the pioneer oil-miners did not have the drilling-machinery ofthe present day, and that they possessed a very limited knowledge concerningthe geological conditions pertaining to the occurrence ofpetroleum-deposits. The pioneer distillers appear to have expected that by the fractionaldistillation of California petroleum they would obtain similar products tothose resulting from the fractional distillation of the petroleum found in theEastern States; but they were disappointed. It is not surprising that, i11 the course of years, the smaller operators became merged in larger concerns. In1887, when the State Mining Bureau made a reconnaissance of thepetroleum-industry of California, the only companies actually engaged inpetroleum-mining were: The Pacific Coast Oil Co. in Pico canon and the PuenteOil Co. in the Puente hills, Los Angeles county; the Hardison and Stewart OilCo., subsequently incorporated as the Union Oil Co., of Ventura county; andMcPherson &Co., operating in Moody Gulch, in Santa Clara county. AIME 029–53
Gas in the St. Lawrence Valley Natural gas has been known to exist for many years in the St. Lawrence Valley, between Quebec and Montreal, and more particularly in the vicinity of Louisville and Three Rivers, 74 and 94 miles respectively northeast ofMontreal, and 98 and 78 miles respectively southwest of Quebec; the distancefrom Montreal to Quebec along the St. Lawrence River being about 175 miles. It was not until 1880 that any practical explorations were begun with the hopeof finding gas in sufficient quantities for commercial uses. In this yearMessrs. Piret and Genest, of Three Rivers, sank a well near St. Maurice to adepth of 50 feet, where solid rock was encountered. A similar well was drilledthrough the glacial and alluvial drift, in the same district, in 1883, by theMessrs. Renaud Freres and Dubois, to a depth of 70 feet before solid rock wasencountered. In this latter well a strong flow of gas was obtained. The gas wasan outflow from a very limited reservoir in the porous glacial gravel, whichhad been filled from the gas resulting from the decomposition of vegetableremains, which had been buried in the gravel at the time of its deposition.Subsequently, other wells were sunk in the same way, with the hope of gettinggas in commercial quantities from similar reservoirs. Commercial Gas- By gas in commercial quantities I mean gas in such quantitythat, if utilized with proper care and economy, it would generate steam at acost below the cost at which the same duty could be obtained from the use ofcoal or wood at current prices, and that the net revenue from the use of thegas would be such as to give a reasonable profit on the capital invested in thedrilling of the well and the piping of the gas to the consumer, and at the sametime provide for a sinking fund to replace this invested capital within thetime when it might be considered that the gas-producing rock would becomeabsolutely exhausted. It is important in this connection to bear in mind thatnatural gas, like all other mineral deposits, can be exhausted. In a commercialsense a gas-reservoir is not unlike a coal-bed. For every cubic foot of gastaken out of a gas-reservoir there is just one cubic foot less remaining. A popular impression exists that the gas is being continually produced, butthis is not a fact in a commercial sense, as far as the natural gas-deposits ofthe Appalachian region are concerned. Natural gas and petroleum are intimatelyassociated with one another. In all gas-reservoirs it is possible to findpetroleum, sometimes, however, in such infinitesimal quantities that it is ofno commercial value, and can only be found by a very careful examination of thegas-producing rock. Natural gas is also always to be found in the rocks whichproduce petroleum, although in the latter case the amount is so small as not tobe practically valuable. AIME 018–35
The occurrence of oil and gas-springs in the State of New York has been afact of historical record since 1627, when the existence of the Cuba oil-springwas first recorded. The utilization of natural gas at Fredonia in 1821 attracted the attention of the public to the possibility of obtaining anilluminating gas by digging and drilling into the rocks. No active search wasmade, however, for oil or gas by the drilling of wells until after thediscovery of commercial oil in Pennsylvania in 1859. In 1862 a well was drilled at Bradford, McKean County, Pennsylvania, but a fewmiles south of the New York state line, to the depth of 200 feet, in search ofthe oil-sand which had been found at Titusville, Oil City, and at other pointsin Western Pennsylvania. Immediately subsequent to this, other wells weredrilled in search of petroleum at a number of points in New York, Particularlyin the western part of the State. Some explorations have been made, in anunsystematic way, for oil ever since, explores being much encouraged in theirsearch by the development of the Allegany oil-district in 1879 and 1880.Immediately subsequent to the general utilization of natural gas inPennsylvania in 1882 and 1883, a new interest was taken in the drilling ofexploration wells, more particularly in search of gas. The principal object of this paper is to publish a record of the explorationswhich have been made up to date for oil and gas in the State. I have notmentioned every well which has been drilled, but only the more important oneswith which I am familiar. The record of these wells have a two-fold value, first, to the practical geologist and well-driller, to enable him to deduceconclusions as to the possibility of getting natural gas in special localities, and to aid in further explorations; and second, to the technical geologist, ingiving definite facts having a direct bearing upon the stratigraphy of thePaleozoic rocks throughout the State. AIME 016–74
Within the last few months much interest has been excited by what is knownas the "anticlinal theory" of gas, a theory so simple, so plausible, and so easily understood by everyone, that its adoption by the gas-producer wasan almost foregone conclusion. The public has also accepted, but not sogenerally, the assertion that the gas exists underground under any necessarypressure as a liquid, thus accounting for the enormous quantities of gasobtained, apparently, from a small area. Some, however, explain this bysupposing that the manufacture of gas is constantly going on in the formationsunderlying the gas-sand. It has also been asserted that the gas may exist(where the rock is not porous) in crevices, and that these crevices or fissureswill be found largely developed along the anticlinal axes. On the other hand, we have the opinion expressed by Professor Lesley that gas, water and oil existing underground at great pressure will not separate, butthat the gas will exist in solution, "mixed" like carbonic acid gas ina soda-water fountain. This hypothesis, if correct, is fatal to the anticlinaltheory. The anticlinal theory would also become less plausible if it were shown thatthe gas exists as a liquid. The difference in specific gravity between it andwater might not then seem sufficient to force each through miles of pores untilthe hydrocarbon liquid had found its way to the crest of the anticlinal, andthe water to the lower portions of the rock, since these rocks, even in thevicinity of the anti- clinal axes, have a very gentle inclination, commonlyless than one degree and very rarely exceeding one degree and a half. We may dismiss this consideration for the present, for it will be seen furtheron that the gas cannot exist as liquid but even if this were not so, time onlywould be required to effect separation. The supposition of continuous manufacture in rocks underlying he gas sands isentertained by few who are familiar with the phenomena presented by oil andgas-wells. The geologist is not able to deny the possibility of this state of affairs: but even if such be the case, the limited life of many gas-wells asgreat producers is sufficient evidence that the natural production undergroundcan only be a fraction of the rate of consumption. AIME 015–13
The existence of natural gas-springs in Pennsylvania and the adjoiningStates west of the crest of the Allegheny Mountains was known to the earliestsettlers. Possibly the first gas obtained from a well was at Fredonia, Chautauqua County, N.Y., where a well was sunk on the bank of Canadaway Creek, near the Main Street bridge, in 1821, and sufficient gas obtained for 30 burners, the inn having been illuminated by the gas when General Lafayettepassed through the village about 1824. In 1858 another well was drilled, whichsupplied 200 burners. A still larger one was drilled to a depth of 1200 feet in1871. According to Mr. E. J. Crissey, Secretary of the Fredonia Natural GasLight Company, the average monthly supply of these wells in 1880 was 110,000 cubic feet. Since 1859, when the drilling of oil-wells in Western Pennsylvania wascommenced, natural gas has been obtained either in conjunction with oil or inwells which produced only a trace of oil. In most of the flowing oil-wells, thepressure which forces the oil up the well results from the gas contained in theoil-sand in the immediate vicinity of the well or at a considerable distanceaway. In the former case, gas is frequently mixed up with the oil as itintermittingly flows from the well-mouth, the gas coming from the wellcontinuously between the oil-flows; while in the latter case, no perceptiblequantity of gas is obtained from the well. I believe that, by specialexamination, all the oil coming from the Pennsylvania and New York wells may beproved to contain some gas. The product of gas-wells has been utilized in various ways, particularly forlight and fuel at the towns and villages in the immediate vicinity of thewells, and also to a limited extent for the manufacture of lampblack sometimescalled "diamond black" by the deposition of the carbon resulting from theimperfect combustion of the gas. A comparatively small proportion of all thegas produced in the region, however, was ever made use of until within twoyears, when the introduction of gas into the industrial establishmentsprincipally iron, steel, and glass-works-in the vicinity of Pittsburgh havemade its use as a fuel an important consideration in the manufacturingindustries of Western Pennsylvania. The geology of the oil-regions of Pennsylvania has been carefully studiedduring the past ten years by the geologists of the Pennsylvania survey, butmore particularly by Mr. John F. Carl, who, since the commencement of theSurvey in 1874, has been in charge of the special examination of thatdistrict. AIME 014–49