12 Geothermal
Resources
地质学：介绍地热的开发利用
导读
地热是来自地球内部的一种能量资源。地球上火山喷出的熔岩温度高达1200℃～1300℃，天然温泉的温度大多在60℃以上，有的甚至高达100℃～140℃。这说明地球是一个庞大的热库，蕴藏着巨大的热能。这种热量渗出地表，于是就有了地热。地热能是一种清洁能源，是可再生能源，其开发前景十分广阔。本文主要介绍了地热的开发利用。
The energy contained in rock within the Earth's crust represents a nearly unlimited energy source, but until recently commercial retrieval has been limited to underground hot water and/or steam recovery systems. These systems have been developed in areas of recent volcanic activity, where high rates of heat flow cause visible eruption of water in the form of geysers and hot springs. In other areas, however, hot rock also exists near the surface but there is insufficient water present to produce eruptive phenomena. Thus a potential hot dry rock (HDR) reservoir exists whenever the amount of spontaneously produced geothermal fluid has been judged inadequate for existing commercial systems.
As a result of the recent energy crisis, new concepts for creating HDR recovery systems—which involve drilling holes and connecting them to artificial reservoirs placed deep within the crust—are being developed. In all attempts to retrieve energy from HDR's, artificial stimulation will be required to create either sufficient permeability or bounded flow paths to facilitate the removal of heat by circulation of a fluid over the surface of the rock.
The HDR resource base is generally defined to include crustal rock that is hotter than 150℃, is at depths less than ten kilometers, and can be drilled with presently available equipment. Although wells deeper than ten kilometers are technically feasible, prevailing economic factors will obviously determine the commercial feasibility of wells at such depths. Rock temperatures as low as 100℃ may be useful for space heating; however, for producing electricity, temperatures greater than 200℃ are desirable.
The geothermal gradient, which specifically determines the depth of drilling required to reach a desired temperature, is a major factor in the recoverability of geothermal resources. Temperature gradient maps generated from oil and gas well temperature-depth records kept by the American Association of Petroleum Geologists suggest that tappable high-temperature gradients are distributed all across the United States. (There are many areas, however, for which no temperature gradient records exist.)
Indications are that the HDR resource-base is very large. If an average geothermal temperature gradient of 22℃ per kilometer of depth is used, a staggering 13,000,000 quadrillion B.T.U.'s of total energy are calculated to be contained in crustal rock to a ten-kilometer depth in the United States. If we conservatively estimate that only about 0.2 percent is recoverable, we find a total that is comparable to the estimated resource base of all the coal remaining in the United States. The remaining problem is to balance the economics of deeper, hotter, more costly wells and shallower, cooler, less expensive wells against the value of the final product, electricity and/or heat.
地球地壳岩石中的能量代表一种几乎是无尽的能源，但是直至最近，商业回收工作一直局限于开发地下热水或者地下蒸汽的回收系统。这些系统是在新近火山活动区开发出来的。在这些地区，高速度的热流以间歇喷泉和温泉的可见形式喷发出来。可是，在其他地区，接近地面也存在有热岩，但缺乏足够的水以产生喷发现象。这样，每当自发产生的地热流量被鉴定为不足以为现行商业系统所利用时，就存在一个可能的干热岩库。
由于最近的能源危机，关于建立干热岩库回收系统的新概念正在形成。这个回收系统必须包括钻洞，并把所钻的洞跟置于地壳深处的人造蓄热库联结起来。在所有试图从干热库回收能源的努力中，人工的刺激是必要的，为的是创造充分的渗透度，或建造封闭的流道，以推进通过岩石表面的流体环流来回收热能。
干热岩源区一般规定为包括热度超过150℃、深度小于10千米、能用现在可以得到的设备来钻探的地壳岩石。虽然深度大于10千米的井孔在技术上是行得通的，但是流行的经济因素显然会决定钻井深度的商业上的可行性。岩石温度低于100℃可用于空间加热；可是为了发电，合乎需要的温度要高于200℃。
具体决定达到预定温度所需钻探深度的地热梯度是回收地热能源的主要依据。根据美国石油地质学家协会所保存的根据油气井温度记录绘制出来的温度梯度变化曲线图表明：可开发的高温梯度区分布在美国全国各地（不过，有许多地区还没有温度梯度记录）。
有开采价值的矿苗表明，干热岩源区是很大的。假如用平均地热温度梯度每千米深度22℃来估算，那么美国10千米深度的地壳岩石所含的总能量为13000000亿亿英国热量单位，这是一个令人惊愕的数字。假如按保守的估算，只可回收大约0.2%的话，那么其总量相当于美国现存估算的全部煤炭资源。剩下的问题是如何权衡更深更热而费用更大的热源井与较浅较冷而费用较小的热源井同最终产品（电力和热能，或者是电力或热能）的价值之间的利害得失关系。
Sentence Translation
句子翻译
1. These systems have been developed in areas of recent volcanic activity, where high rates of heat flow cause visible eruption of water in the form of geysers and hot springs.
2. The geothermal gradient, which specifically determines the depth of drilling required to reach a desired temperature, is a major factor in the recoverability of geothermal resources.
Key
1．这些系统是在新近火山活动区开发出来的。在这些地区，高速度的热流以间歇喷泉和温泉的可见形式喷发出来。
2．具体决定达到预定温度所需钻探深度的地热梯度是回收地热能源的主要依据。