【摘要】：開發(fā)致密氣藏,生產井通常需要經過水力壓裂才能實現工業(yè)化開采。通過泵入大量混有支撐劑的壓裂液到地層中,形成一條導流能力較高的支撐裂縫,改善氣體流入井筒的滲流通道,從而提高單井產能和最終采收率。但是,由于各種原因,低滲氣井產能遠遠小于我們的預測產能。通過大量研究發(fā)現最重要的原因就是有效縫長小于設計縫長。形成這種短縫的原因是縫高失控、裂縫端部脫砂、支撐劑分布不合理、支撐劑回流,也有可能是受它們的綜合影響。當然,這也有可能是因為壓裂液破膠不徹底而導致壓裂液返排太慢。眾所周知,當壓裂施工結束后,仍然有部分壓裂液殘留在裂縫和地層當中,降低了侵入帶地層的有效滲透率從而導致氣井產能的降低。因此,為了提高壓裂效果,必須保證地層中盡可能少的壓裂液殘余量。然而,裂縫導流能力與有效縫長的影響關系還不是很明確。因此,研究導流能力與有效縫長的關系,給出合理的導流能力和有效縫長,對后期壓裂優(yōu)化設計,實現致密氣藏高效開發(fā)具有重大意義。在壓裂設計中,我們一般將支撐縫長(設計縫長)定義為有效縫長。然而,致密氣藏普遍具有超低含水飽和度現象,壓后在裂縫附近地層易形成水相圈閉區(qū),阻礙了氣體向裂縫中的流動,真實的有效縫長也就小于設計縫長。本文中將有效縫長定義為對氣井產能有實際貢獻的裂縫長度(有氣體流入的裂縫長度)。本文對中江沙溪廟組的靜動態(tài)地質特征進行分析,結果表明該區(qū)直井低產的主要原因是侵入帶氣體相對滲透率較低、有效縫長小于設計縫長。對該區(qū)S1井進行加砂壓裂,一周后進行壓力恢復測試,測試結果表明該井外推地層壓力為47.6252MPa,地壓系數1.68,與原始地層壓力相近。然而,分析得出的地層有效滲透率只有0.00468×10-3μm2,遠小于實際值0.18×10-3μm2,有效縫長只有17m,為設計縫長的8.9%,更加驗證了致密砂巖儲層水相圈閉區(qū)域的存在。壓裂液的侵入增加了裂縫侵入帶的含水飽和度,從而降低了氣體的相對滲透率,過短的有效縫長更是導致了實際產能低于預測產能。然而,致密砂巖儲層普遍具有超低含水飽和度現象(實際含水飽和度低于最小含水飽和度),目前我們無法完全消除水相圈閉對致密氣藏的傷害,因此我們只能盡可能的增加壓裂液的返排來最大限度的增加有效縫長,提高氣體產能。我們借助油藏數值模擬技術,通過建立氣水兩相二維模型來研究在不同地層滲透率、不同裂縫半長、不同濾失量及不同裂縫侵入帶傷害程度四種條件下裂縫導流能力對有效縫長的影響。通過氣體流入裂縫累計分布曲線圖和多種導流能力條件下不同生產時間點的有效縫長對比圖來分析氣體沿支撐裂縫的分布情況以及各種影響因素下,導流能力對有效縫長的影響。研究表明,研究區(qū)沙溪廟組具有較好的地質資源和良好的勘探開發(fā)前景。壓裂液的侵入對于裂縫侵入帶氣體的相對滲透率造成了重大傷害。開采初期,有效縫長遠小于設計縫長,隨著生產時間的增加有效縫長在1年后基本都能接近設計縫長。盡管氣體沿著整條裂縫流動,但是殘留在裂縫侵入帶中的壓裂液不可能完全返排出來。含水飽和度的分布影響著氣體向裂縫的流動速度,甚至決定有效裂縫的長度。氣體流動效率的輕微的改變將對有效裂縫長度的變化起著非常大的影響。換而言之,裂縫導流能力越大,壓裂液返排就更加徹底,有效縫長就會更長,增產效果就會更加明顯。
[Abstract]:In the development of tight gas reservoirs, production wells usually need hydraulic fracturing to realize industrial production. A high conductivity supporting fracture is formed by pumping a large amount of fracturing fluid mixed with proppant into the formation, which improves the percolation channel of gas into the wellbore, thereby increasing the single well productivity and ultimate recovery. The productivity of low permeability gas wells is far less than our predicted productivity.The most important reason is that the effective fracture length is less than the designed fracture length.The causes of this kind of short fracture are uncontrolled fracture height,desanding at the end of the fracture,unreasonable proppant distribution,proppant reflux and their comprehensive influence. It is well known that some fracturing fluids remain in fractures and formations after fracturing operation, which reduces the effective permeability of the formation in the intrusive zone and leads to the decrease of gas well productivity. Therefore, in order to improve the fracturing effect, it is necessary to ensure as little as possible in the formation. However, the relationship between fracture conductivity and effective fracture length is not very clear. Therefore, it is of great significance to study the relationship between fracture conductivity and effective fracture length, and to give reasonable conductivity and effective fracture length for later fracturing optimization design and efficient development of tight gas reservoirs. Supporting fracture length (designed fracture length) is defined as effective fracture length. However, compact gas reservoirs generally have ultra-low water saturation. Water-phase traps are easily formed near fractures after compression, which hinder gas flow into fractures, and the actual effective fracture length is less than the designed fracture length. In this paper, the static and dynamic geological characteristics of Shaximiao Formation in Zhongjiang are analyzed. The results show that the main reason for low production of vertical wells in this area is that the relative permeability of gas in the intrusion zone is low and the effective fracture length is less than the designed fracture length. The test results show that the extrapolated formation pressure is 47.6252 MPa and the ground pressure coefficient is 1.68, which is similar to the original formation pressure. However, the analysis shows that the effective permeability of the formation is only 0.00468 6550 The invasion of fracturing fluid increases the water saturation of the fractured intrusive zone, which reduces the relative permeability of the gas. The short effective fracture length leads to the fact that the actual productivity is lower than the predicted productivity. We can not completely eliminate the damage of water trap to tight gas reservoir before, so we can only maximize the effective fracture length and improve gas productivity by increasing fracturing fluid flowback as much as possible. The influence of fracture conductivity on effective fracture length under four conditions, i. e. different filtration rate and different damage degree of fracture invasion zone. The gas distribution along supporting fracture and various influencing factors are analyzed by the cumulative distribution curve of gas inflow fracture and the effective fracture length contrast chart of different production time points under various flow conductivity conditions. The results show that the Shaximiao Formation in the study area has good geological resources and good prospects for exploration and development. The invasion of fracturing fluid causes great damage to the relative permeability of gas in the fracture-invaded zone. Although gas flows along the entire fracture, the remaining fracturing fluid in the fracture-invading zone can not be completely discharged. The distribution of water saturation affects the velocity of gas flowing into the fracture, and even determines the length of the effective fracture. In other words, the greater the fracture conductivity, the more thorough the fracturing fluid backflow, the longer the effective fracture length, and the more obvious the stimulation effect.
【學位授予單位】：成都理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TE377

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本文編號：2205358