A Model for Calculating Annular Pressure Loss in Slim Hole Taking into Account Tool Joint
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摘要: 小井眼钻井作为开发深部油气资源的重要技术手段越来越受到重视。小井眼往往具有更高的环空压耗,这给环空压力控制带来了一定挑战。准确预测钻柱偏心旋转情况下的环空压耗是小井眼钻井的重要理论与实践基础,但常规预测模型适用性非常有限,往往忽略了钻杆接头的影响,无法满足现场的精度需求。为此,利用数值模拟技术,分析了钻杆接头对环空流场、压耗的影响规律,并据此确定了压耗修正因子经验模型的构建方式。分析结果表明:钻杆接头所产生的额外压耗受钻井液类型、钻杆转速、偏心和环空返速的影响,压耗修正因子的构建应考虑多种因素的耦合关系。利用152组数模结果,建立了针对新疆玛湖油田的小井眼环空压耗预测模型,该模型计算结果表明,在钻杆低偏心度情况下存在临界转速,使得环空压耗达到最大,而钻杆处于高偏心度时,环空压耗会随转速增大而增大;而偏心度对环空压耗的影响规律也会因转速不同而变得更加复杂。利用环空压耗预测模型,计算了玛湖油田MHHW-X井的当量循环密度,结果与PWD数据进行对比,平均误差仅为1.18%,模型具有较高的准确性。研究结果表明,利用数模结果建立的考虑钻杆接头的小井眼环空压耗模型可以满足现场预测精度需要,能够为现场环空压力控制提供指导。Abstract: Slim hole drilling as an important technology is more and more used in developing deep oil and gas resources. In slim hole drilling, the much higher annular pressure losses impose a challenge to the annular pressure control. Accurate prediction of the annular pressure losses under the condition of eccentric rotation of drill string is an important theoretical and practical base for slim hole drilling. Conventional prediction models for this purpose have limited applicability and often omit the influences caused by the tool joints, thus cannot satisfy the requirements for accuracy in field operation. To solve this problem, a method of constructing empirical models with pressure loss correction factors is established based on the analyses of the effects of the tool joints on the flow-field and pressure losses in annular spaces using numerical simulation. The analyses show that the extra pressure losses produced by the tool joints are affected by the type of drilling fluid, rotary speed of drill pipe, eccentricity of drill pipe and annular flow velocity. Thus, when determining the pressure loss correction factor, the coupling of these effects should be taken into account. Using the result of numerical simulation of 152 sets of data, a model for predicting the annular pressure losses of the slim holes drilled in the Mahu oilfield in Xinjiang is established. The calculation using this model shows that there is a critical rotary speed at low drill pipe eccentricity, at which the annular pressure loss reaches maximum. At high drill pipe eccentricity, the annular pressure losses increase with rotary speed. The effects of the drill pipe eccentricity on the annular pressure losses will become complex because of the rotary speed. Using the annular pressure loss prediction model developed, the equivalent circulation density of the well MHHW-X in the Mahu oilfield was calculated and compared with the PWD data, the average error was only 1.18%, indicating that the model has high accuracy. The results of the study show that, the model established through numerical simulation for calculating annular pressure losses in slim holes, which takes into account the effects of tool joints, is able to satisfy the requirement of accuracy for field prediction of annular pressure losses, and to provide guidance to the annular pressure control in field operation.
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Key words:
- Annular pressure loss /
- Slim hole /
- Tool joint /
- Drill pipe rotation /
- Eccentricity /
- Prediction model
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表 1 玛湖区块现场钻井液流变参数
井号 K/Pa·sn n τ/Pa 1 0.3959 0.6914 2.550 2 0.6966 0.5741 1.530 3 0.4243 0.7048 3.060 4 0.1067 0.8322 0.511 表 2 混合水平正交实验表
实验组 钻柱转速/
r·min−1钻井液 环空返速/
m·s−1偏心度 压耗梯度模拟值/
Pa·m−1一般模型计算结果/
Pa·m−1Frej 1# 0 1 0.6 0 1036.02 949.13 1.0915 2# 20 1 1.0 0 1402.89 1255.33 1.1175 3# 80 1 1.0 0 1391.81 1255.33 1.1087 4# 100 1 0.6 0 1006.20 949.13 1.0601 5# 40 2 0.6 0 956.01 884.69 1.0806 6# 120 2 1.0 0 1250.42 1141.37 1.0955 7# 60 2 1.0 0 1264.76 1141.37 1.1081 8# 140 2 0.6 0 915.66 884.69 1.0350 9# 40 3 1.2 0 1811.06 1612.69 1.1230 10# 60 3 0.8 0 1398.82 1279.55 1.0932 11# 120 3 0.8 0 1377.62 1279.55 1.0766 12# 140 3 1.2 0 1793.80 1612.69 1.1123 13# 0 4 1.2 0 852.14 694.37 1.2272 14# 20 4 0.8 0 597.98 508.91 1.1750 15# 80 4 0.8 0 594.84 508.91 1.1688 16# 100 4 1.2 0 851.66 694.37 1.2265 17# 40 1 0.8 0.2 1216.72 1108.21 1.0979 18# 60 1 1.2 0.2 1573.56 1393.57 1.1292 19# 20 2 1.2 0.2 1096.57 1019.94 1.0751 20# 0 2 0.8 0.2 1404.71 1252.80 1.1213 21# 80 3 0.6 0.2 1169.27 1094.72 1.0681 22# 100 3 1.0 0.2 1604.80 1451.07 1.1059 23# 120 4 0.6 0.2 479.14 410.53 1.1671 24# 140 4 1.0 0.2 741.11 603.21 1.2286 25# 140 1 0.8 0.4 1604.84 1393.57 1.1516 26# 120 1 1.2 0.4 1215.41 1108.21 1.0967 27# 100 2 0.8 0.4 1424.09 1252.80 1.1367 28# 80 2 1.2 0.4 1115.99 1019.94 1.0942 29# 0 3 1.0 0.4 1454.37 1451.07 1.0023 30# 20 3 0.6 0.4 1077.54 1094.72 0.9843 31# 40 4 1.0 0.4 730.81 603.21 1.2115 32# 60 4 0.6 0.4 480.52 410.53 1.1705 表 3 玛湖油田MHHW-X井井身结构及钻进参数
钻井参数 排量/(L/s) 16 钻杆接头外径/m 0.1240 垂深/m 3526 钻杆接头内径/m 0.0635 测深/m 5719 加重钻杆内径/m 0.0635 钻杆外径/m 0.1651 加重钻杆外径/m 0.1016 钻杆内径/m 0.1016 接头长度/m 0.5100 套管内径/m 0.1750 钻头水眼尺寸/mm 11 -
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