井眼周圍地層滲透率會因鑽井、完井或生產操作等因素而改變，因滲透率改變而造成的壓力變化可用膚表因子表示之。若井眼周圍地層滲透率降低則膚表因子為正值（污損），而滲透率增加則膚表因子為負值（激勵），通常膚表因子為一定值。但實際上油氣井生產時，可能因為清井效應增加井眼周圍地層滲透率（膚表因子降低），或是生產時流體帶動地層顆粒至井眼周圍沉積降低井眼周圍地層滲透率（膚表因子增加）。由於井眼周圍地層滲透率可能會隨時間變化，換言之，膚表因子也會隨時間變化（變膚表因子）。在傳統井壓測試分析中是假設膚表因子為定值，然而探討變膚表因子的井壓測試分析之文獻並不多。因此，本研究的目的是，利用數值模擬軟體，研究定產率生產時，變膚表因子的暫態壓力行為，並利用最佳化法推求變膚表因子和地層滲透率，最後將此最佳化法運用在現場案例中，以求得變膚表因子和地層滲透率。
在變膚表因子對暫態壓力影響之研究，本研究提出四種變膚表因子模型（線性、指數-1、指數-2、與雙曲線），並根據變膚表因子模型建立變膚表因子數值模式後，研究變膚表因子對暫態壓力的影響，之後利用最佳化法分析壓力資料反推求變膚表因子與地層滲透率以驗證本研究最佳化法之正確性。
本研究可獲致結論如下：（1）如果以傳統井壓測試方法分析變膚表因子暫態壓力，若膚表因子隨時間減少會推求出高估的膚表因子及地層滲透率，反之，膚表因子隨時間增加會推求出低估的膚表因子及地層滲透率。但膚表因子若以指數-2隨時間變化，則可利用後段壓力資料推求關井時的膚表因子及地層滲透率。（2）分析現場案例的井壓下降資料時，利用最佳化法的壓力分析結果比傳統井壓下降分析方法更為準確。（3）當現場只有一段井壓下降資料，且壓力變化趨勢與變膚表因子的壓力行為類似，可考慮使用最佳化法進行壓力分析，其膚表因子及地層滲透率的分析結果可信度較高。

The skin factor might represent a pressure drop caused by variations in permeability near the wellbore resulting from drilling, well completion, or production. When the reservoir is infiltrated by mud and drilling fluid near the wellbore, permeability around the well is lowered, and the skin is positive. Conversely, a stimulated well raises permeability and has a negative skin. The skin is generally considered a constant, but, in reality, it may change over time. During the cleanup period in a well test, the skin decreases. Over a long production period, the well may be damaged again, and then the skin increases. Few reports consider a variable （changing over time） skin in well test analysis. Therefore, the purposes of this study are to analyze （1）how a variable skin affects transient pressure and （2）the optimization methods used to estimate variable skin and permeability based on transient pressure data.
Four variable-skin models—linear, exponential-1, exponential-2, and hyperbolic skin—were used to establish numerical models. After numerical simulation, the transient pressure was analyzed using well testing to study the effect of variable skins on transient-pressure analysis, amd then analyzed by optimization methods to vetify the accuracy of optimization methods.
The major conclusions were that：（1）if transient pressure with variable skin was analyzed by tranditional well testing method, skin factor and permeability were overestimated when skin decreasing, while underestimated when skin increasing. （2）In field case, the well testing results of optimization methed is better than tranditional well testing method. （3）pressure data can be analyzed precisely by using optimization methods on condition that pressure trend is similar to pressure tendency with variable skin.

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