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本文介绍了两口井的高孔隙度高渗透率砂岩储层的NMR测井实例。与常规的测井和地层测试结果相比较,NMR测井显示出总共160m厚井段的孔隙度异常和T_2分布谱的异常。NMR孔隙度近似为12p.u.,它低于用一个2.65g/cm~3颗粒密度的密度孔隙度。T_2测井平均分布谱几乎整个低于33ms的截止限。因此,这些NMR响应一般指出毛细管束缚水的孔隙度占主导地位,而自由流体孔隙度很小,说明了储层性能差。它与本地区砂岩的高电阻率、含泥质少、一般认为好的渗透性形成了鲜明的对比。实际上,在一次钻杆测试(DST)中井产油流为3000bbl/d,测量的渗透率为6D。在这两个例子中,从自由流体孔隙度与总的NMR孔隙度的关系中得出的理论电阻率与Rxo测量值符合得相当好,相反地却低于Rt的1/20。NMR可能与在冲洗带的某种影响有关。另外,DST解释指出地层高度受损,其破损比从17变到6。因此,冲洗带的储层孔隙空间中的泥浆内的固态物质降低了NMR孔隙度和T_2分布值。总之,当发生泥浆内的固态物质侵入时,建议不要用NMR代替储层中的密度和中子测井。这种近井孔效应几乎完全发生在NMR仪器的探测范围内。事实也表明,在泥浆内的固态物质侵入到地层的储层中,密度和中子测井同样也受到影响,虽然这种影响程度比较小。测井仪器探测深度越浅,破坏带的影响越大。结果,泥浆内固态物质侵入将导致对地层内原油体积的低估。
This paper presents an example of NMR logging of high-porosity and high-permeability sandstone reservoirs in two wells. Compared with conventional logging and formation testing results, NMR logs show anomalies of porosity and T 2 distribution profiles for a total of 160 m. The NMR porosity is approximately 12 p.u., which is less than the density porosity of a 2.65 g / cm ~ 3 particle density. The T_2 log average profile is almost entirely below the cutoff of 33 ms. Therefore, these NMR responses generally indicate that the capillary bound water dominates the porosity while the free-fluid porosity is small, indicating poor reservoir performance. It is in sharp contrast with the high resistivity of sandstone in the region, with less argillaceous and generally considered good permeability. In fact, the well produces a flow of 3000bbl / d in a Drill Pipe Test (DST) and a measured permeability of 6D. In both cases, the theoretical resistivity derived from the relationship between free fluid porosity and total NMR porosity is in good agreement with the Rxo measurements, but less than 1/20 of Rt. NMR may be related to some influence on the wash zone. In addition, DST explained that the stratum height is impaired, with a breakage ratio of 17 to 6. Therefore, the solid material in the mud in the reservoir pore space of the wash zone reduces the NMR porosity and T 2 distribution values. In summary, it is not recommended to use NMR in place of density and neutron logging in a reservoir when solids in the mud intrude. This near-borehole effect occurs almost entirely within the detection range of the NMR instrument. Facts have also shown that density and neutron logging are also affected by the penetration of solid matter within the mud into the formation reservoir, albeit with relatively little impact. The shallower the logging depth of the logging instrument, the greater the impact of the damage zone. As a result, intrusion of solid material within the mud will lead to an underestimation of the volume of crude oil in the formation.