The Research For The Clastic Rock Shallow Gas Layer Logging Evaluation

According to the regulation of gas reservoir,the gas below 1500m under the ground is called shallow layer gas,so the reservoir of that is regarded as shallow gas layer.Nowadays,shallow layer gas reservoir is attracting gradually the expropriators' sight,because it is shallow,and it is easy and economical to expropriate and develop.The clastic rock shallow gas layer has the characters of lower deep and infirmness compaction, so that the compaction extent of mud and the pressure of pore volume and liquid are low.So,the shallow gas layer has bellowing characters.①porosity,permeability and Swi is relatively high,so that its resistivity is lower.②because of more water in clay of mud and its variety with deep, mud's parameters will change obviously by the buried depth,such as CNL,DEN and R.③logging parameters of natural gas,such as CNL,DEN and AC,will change by the buried depth, which is obviously different from the middle deep gas layer.④the gas reserves of reservoir is not only related to porosity,permeability,Sw and efficient thickness,but also to the gas density. Because gas is always full of the room no matter what its quality.Thus the gas density is very important.Namely,it is gas full degree for reserves,which is such that to shallow gas layer.Just about the basic characters of shallow gas layer,it is different from the routine reserves when logging evaluation choosing parameters.If we don't take notice of the important issue,the logging evaluation misplay will be inevitable.As mentioned above,we have found that its reservoir is different from the routine ones. Nowadays,it also introduces to the routine logging method to the evaluation for the Clastic rock shallow gas layer,so,its evaluation result is irresponsible.including three facets.Frist,the account result error of reserves parameters is higher because of disaccurately considering the mud contribution to the logging well response.Second,the misplay to liquid character differentiation is more because of the gas parameters variety.Third,be incapacitated for confirming the gas quality,and do the gas suffuse degree in the reservoir.So,it's not only to affect the misplay to liquid character differentiation according to theΦ_N excavation effect,but also to make the error of the gas layer reserves.So,the paper has researched the mud adjusting model and chart of the clastic rock shallow gas layer,analyzed the swi sense and affecting factor,discussed the application condition and limitations of the present swi synthetical menthod,provided the new Swi menthod based on routine logging datum,provided the suffuse degree,and researched the reservoir's gas density model,formation pressure model and the suffuse degree model.Finally,the paper has researched the software program and application study of the clastic rock shallow gas layer evaluaterating method.I have acquired the following recongnization and conclusion according to the research result.(1) The mud's DEN,CNL,AC and R parameters of the clastic rock shallow gas layer are different from the middle & depth gas layer,and they are vary with the depth according to the mud adjusting model and chart of the clastic rock shallow gas layer.(2) About the fluid type distinguish,it should together distinguish with the Sw and Swi parameters,and the key is to account Swi.(3) The new Swi menthod based on routine logging datum,is based on the drilling fluid's intrusion feature to the reservoir and the realition between intrusion-related zone's drilling fluid filtrate,the irreducible water resistivity and the Swi.And the Swi is comprehensively calculated by the routine logging datum.The method hardly affects with the area,and does expediently account,then we have obtain the obvious result to the application.So,it is better than the genergal statistical method.(4) For one thing,it used to be incline to the gas layer characteristic with the the reservoir curve separation increasing between the porosity and the AC or DEN.But which maybe generate that the high production gas layer is judged to the water layer when the reservoir's gas density is major.For anohter,as to the logging quantity evaluation of the gas layer,which used to be use the porosity,gas saturation,permeability and effective thickness.And it is difficult for the four parameters to evaluate the reservoir's gas production rate,so,it must be intorduce the suffuse degree parameter which is mutually related the gas density to together evaluate.(5)It's the first time to provide the suffuse degree,which is the gas ratio between the formation temperature and pressure and the ST(293K or 20℃) and base pressure(0.101Mpa). Thus the new method to calculate the reservoir pressure occurs with the reservoir static state logging parameters,then it has realizen the gas layer with the reservoir static state feature and the dynamic feature.(6) According to the evaluation method of the clastic rock shallow gas layer applying into the Baima and Songhua shallow gas layer,the new Swi menthod based on routine logging datum can accurately calculate the Swi,and accurately distinguish the fluid type.And the reservoir gas production rate is positive correlation with the suffuse degree,and it can be evaluated with the suffuse degree combination with the porosity,gas saturation,permeability and effective thickness. The method is also fit for the Sulige gas field whose layer is middle deep gas ones,so,it can popularize and apply to the other gas field.(6) With the evaluation method of the clastic rock shallow gas layer,it can accurately calculate the Swi and accurately distinguish the fluid type.And it also can evaluate the reservoir gas production rate with the suffuse degree combination with the porosity,gas saturation, permeability and effective thickness.We have acquired the goog effectiveness not only in the Baima and Songhua shallow gas layer,but also in the Sulige gas field whose layer is middle & deep gas ones.So,which shows that the method can popularize and apply to others gas fields.